text:
# Detect Time Travel

Computers are everywhere nowadays - in cars, trains, skateboards, even nuclear reactors. The possibility that your software will run in a time travelling device is just a matter of time. Can you deal with it? Can you at least detect it?

1. Write a program that loops and keeps querying the system time, in order to detect time travel.
2. If time moves forward a day or more between two consecutive queries, it's forward time travel. In this case, your program should print:
TS TS: YYYY? You mean we're in the future?
3. If time moves back, by any amount, between two consecutive queries, it's backward time travel. In this case, your program should print:
TS TS: Back in good old YYYY.
4. TS TS are the timestamps before and after the time travel. YYYY is the destination year.
5. Timestamps may be in any format, that includes at least the 4-digit year, month, day, hour, minute and second, separated by non-digits.

Limitations:

1. You must support dates in the 19th, 20th and 21st centuries, at least.
2. You must use a language that existed before this challenge was posted.
3. You must post your answers only after this challenge was posted.
4. You must use a language that existed before your answer was posted.
6. Your program must not print any output other than the required output. An occasional "Great Scott!" is allowed.

This is code-golf. The shortest answer wins.

• More falsehoods programmers believe about time, #36: "Time always goes forwards."
– Doorknob
Oct 21 '15 at 11:40
• Could you be a bit more specific about #5?
– user45941
Oct 21 '15 at 13:27
• separated by nondigits? boo. YYYYMMDDHHmmSS is my favorite timestamp format. Oct 21 '15 at 17:13
• @Aequitas how do you know? maybe the system clock is actually immutable and "setting" it is actuallly time traveling Oct 22 '15 at 5:42
• Limitation 2,3,4,5 are really harsh, I don't know if I can handle that.
– Surt
Oct 23 '15 at 0:10

## Python 2, 210 bytes

from datetime import*
o=0
while 1:n=datetime.now();o=o or n;print"%s;%s: %s? You mean we're in the future?"%(o,n,n.year)if(n-o).days>=1else"%s;%s: Back in good old %s."%(n,o,n.year)if(n<o)else"Great Scott!";o=n

Timestamps are printed in in YYYY-MM-DD HH:MM:SS format, separated with semicolons. Switched to Python 2 from 3 since it's 2 chars shorter to print. Spams stdout with Great Scott! for normies non-time-travellers, since it's easier and cheaper to do that than set up a conditional print.

• Does it expect the time as input? This is not what's asked (maybe it's vague). Also, it seems to print blank lines when time behaves well. Oct 21 '15 at 12:18
• I meant asking the OS, not the user. I'll clarify. Oct 21 '15 at 12:21

# JavaScript (ES6), 263 bytes

n=Date;o=n.now();(function g(){k=new n;j=new n(o);s=${k}${o} ;if(n.now()-o>86400)console.log(${s}${k.getFullYear()}? You mean we're in the future?);if(o-n.now()>84600){console.log(${s}Back in good old${k.getFullYear()}.);}o=n.now();setTimeout(g,100);}());

This could probably do with some rewriting to make it more efficient/small.

Source:

n=Date;
o=n.now();

(function go() {
k=new n;
j=new n(o);
s=${k}${o} ;
if (n.now() - o > 86400) {
console.log(${s}${k.getFullYear()}? You mean we're in the future?);
}
if (o - n.now() > 84600) {
console.log(${s}Back in good old${k.getFullYear()}.);
}
o=n.now()
setTimeout(go,100);
}());

• Backwards travel is defined as moving back by any amount, not one day. Also, due to the multiple now() calls it may miss a travel event. Oct 21 '15 at 12:21
• An attempt at golfing this: n=Date,o=n.now();setInterval("d=new n,s=d+ ${new n(o)} ;f=d.getFullYear();if(n.now()-o>8.64e+7)console.log(s+f+? You mean we're in the future?);if(o>n.now())console.log(s+Back in good old${f}.);o=n.now()",100); Oct 21 '15 at 13:49
• I think you can golf the first part to o=(n=Date).now(). Oct 21 '15 at 17:22
• +Stefnotch 8.64e+7 is two characters longer than 86400. Oct 21 '15 at 17:28
• @CᴏɴᴏʀO'Bʀɪᴇɴ Oops! I was wondering why it didn't work. Oct 21 '15 at 19:24

# Python 3, 195

from datetime import*
n=datetime.now
p=n()
while 1:
c=n();f=(p,c,p.year);s=(0,("%s %s: %s? You mean we're in the future?"%f,"%s %s: Back in good old %s."%f)[p.day>c.day])[p>c];p=c
if s:print(s)

Currently doesn't print Great Scott because I can't find a good way of only making it occasional.

d()(date -d@"$@") for((b=date +%s;a=date +%s;b=a)){ t=d$a\ d $b ((a<b))&&d$b "+$t: Back in good old %Y." ((a>b+86400))&&d$b "+$t: %Y? You mean we're in the future?" }  # CJam, 118 bytes et:Tes{es_@-[TS*Set:TS*':S]\_864e5<{[1$et0="? You mean we're in the future?"N]o}|0<{[_"Back in good old "et0='.N]o}&}g

This does not work with the online interpreter.

Sample output after adjusting my computer's time twice:

2015 10 21 11 2 45 1 3 -10800000 2015 10 23 11 2 45 0 5 -10800000: 2015? You mean we're in the future?
2015 10 23 11 2 53 448 5 -10800000 2015 10 21 11 2 52 0 3 -10800000: Back in good old 2015.

• Why doesn't it work with the online interpreter (except that it doesn't let you fiddle with the time)? Oct 25 '15 at 7:51
• Because this is an infinite loop, and the online interpreter shows output only after the program has finished. Oct 25 '15 at 13:12
• So how do you test that it works? Oct 25 '15 at 16:16
• Using the Java interpreter. Oct 25 '15 at 16:20

# Ruby, 194 bytes

I haven't had the time to really cut this down to size yet. I'm sure there are a few optimizations hiding in there.

require 'time';t=nil;while 1;n=Time.now;if t;s="#{t} #{n}: ";y=n.year;puts t>n ? "#{s}Back in good old #{y}" : (n>t+86400 ? "#{s}#{y}? You mean we're in the future?": "Great Scott!");end;t=n;end

Ungolfed (and a lot more readable):

require 'time'
t=nil
while 1
n=Time.now
if t                                             # on second or later pass
s="#{t} #{n}: "                                # prepare the timestamp
y=n.year
puts t>n ?                                     # if we go back
"#{s}Back in good old #{y}" :                # timestamp + phrase
(n>t+86400 ?                                 # else, more than one day forward
"#{s}#{y}? You mean we're in the future?": # timestamp + future
"Great Scott!")                            # Great Scott!
end
t=n                                              # set a new jump point
end

Edit: corrected to ask OS for time, rather than a human.

• A few recommendations: Use loop{} instead of while 1...end, and try using + for string concatenation instead of interpolation. Oct 22 '15 at 0:25

# Lua 5.3, 174 bytes

T=os.time P=print l=T()::a::t=T()b=l.." "..t..": "y=os.date('%Y',t)_=t<l and
P(b.."Back in good old "..y)or t>l+86399 and
P(b..y.."? You mean we're in the future?")l=t goto a

This is playing heavily off of the "Timestamps may be in any format" rule ... which I took the liberty of using the format of "seconds since Jan 1, 1970"

If I keep my shoddy interpretation of printing timestamps, and adopt the structure of MeepDarknessMeep, I can (unethically) squeeze this down to ...

# 155 bytes

T=os.time::G::l=t or T()t=T()_=(t>l+86399or t<l)and
print(l.." "..t..": "..os.date(t<l
and"Back in good old %Y"or"%Y? You mean we're in the future?"))goto G

• Timestamps may be in any format, that includes at least the 4-digit year, month, day, hour, minute and second, separated by non-digits. - that doesn't allow seconds since epoch.
– user45941
Oct 21 '15 at 13:15
• good thing it didn't "exclude" any formats Oct 21 '15 at 13:19
• @ugoren Really that requirement should be more specific as to your intention
– user45941
Oct 21 '15 at 13:21
• I'm not fully familiar with lua so I may be wrong, but it looks like this prints Back in good ol YYYY but it should print Back in good old YYYY. (Note the d in old) Oct 21 '15 at 15:39
• nope good catch, I was trying to shave bytes wherever I could :-p Oct 21 '15 at 16:31

# Lua 5.3, 179178173171169168 163 bytes

q="%Y %c: "c=os.date::a::d=f f=os.time()_=d and(f-d>86399or f<d)and print(c(q,d)..c(q..(f<d and"Back in good old %Y."or"%Y? You mean we're in the future?")))goto a

Side note: If you take out the need for a full year number then subtract six bytes. The reason is that lua's (or windows' or someone's!) %c doesn't output the full year. Because of this, the timestamps may look weird!

This also takes advantage of timestamps being able to be seperated by any non digit characters!

Thanks for notifying me of my old math.abs reference and other improvements @thenumbernine :)

# Lua 5.3, 151 bytes

This is 'copying' off of @thenumbernine's method of displaying time by just showing the timestamp instead of the actual date. This isn't competitive since I think it is a bit of cheating, just posting it here to display my work :)

::a::d=f f=os.time()_=d and(f-d>86399or f<d)and print(d.." "..f..os.date(f<d and": Back in good old %Y."or": %Y? You mean we're in the future?"))goto a

• We posted both our Lua answers at nearly the exact same time. That has to say something about time travel. Oct 21 '15 at 13:13
• Ahah, Thanks @thenumbernine! I finally got my ability to comment :) Oct 21 '15 at 13:43

# Python, 170 165 bytes

from datetime import*
n=datetime.now
c=n()
while 1:
p=c;c=n()
if(c-p).days:print p,"%s:"%c,["%s? You mean we're in the future?","Back in good old %s."][c<p]%c.year

This owes a lot to Morgan Thrapp's answer. The main trick here is timedelta normalization, which conveniently makes timedelta.days negative when moving even slightly towards the past, and 0 when moving less than a day to the future.

• After import* you don't need the datetime. prefix. Oct 25 '15 at 10:21
• @ugoren: import* allows one to write datetime.now() instead of datetime.datetime.now(). It kind of makes sense, in a way...
– han
Oct 25 '15 at 11:44
• In a confusing way, it does. Oct 25 '15 at 16:16

# Caché ObjectScript, 199 bytes

l s k=86400 f  s e=+$H,t=$P($H,",",2) s:'d d=e,s=t s z=$ZDT(h)_" "_$ZDT($H)_": ",y=h\365+1841 w:e>d !,z,y,"? You mean we're in the future?" w:(k*t+e)<(k*s+d) !,z,"Back in good old ",y s h=$H,d=e,s=t  This problem is solvable in plain old MUMPS, but would be unreasonably lengthy, since ANSI MUMPS lacks the $ZD[ATE]T[IME] intrinsic function for formatting dates into human-readable timestamps.

This program will probably not detect time-travel to before 1 Jan 1841, nor time-travel to after 31 Dec 9999, since these are the bounds of the $H[OROLOG] timekeeping intrinsic. This program also only has second-level precision; sub-second-level backwards time glitches will likely escape its notice. ## TSQL, 355 bytes At the work so no fancy cool languges stick with your SQL Server production server =) Golfed version declare @a datetime=getdate(),@b datetime,@d float,@ char(99),@y char(4)while 0=0begin select @b=getdate(),@d=cast(@b as float)-cast(@a as float),@y=' '+DATEPART(y,@b),@=cast(@a as char(20))+' '+cast(@a as char(20))+': 'if @d>=1set @=@+@y+'? You mean we''re in the future?'if @d<0set @=@+'Back in good old '+@y+'.'print @ set @a=@b end  More readable version with minor changes. declare @t0 datetime = getdate(), @t1 datetime, @d float, @m varchar(99), @y char(4) while 0=0 begin set @t1 = getdate() set @d = cast(@t1 as float) - cast(@t0 as float) set @y = ' ' + DATEPART(yy, @t1) set @m = cast(@t0 as varchar(30)) + ' ' + cast(@t0 as varchar(30)) + ': ' if @d >= 1 set @m = @m + @y + '? You mean we''re in the future?' if @d < 0 set @m = @m + 'Back in good old ' + @y + '.' print @m set @t0 = @t1 end  SQL is not that bad in respect to timestamps since it's a first class data type. For the golf's sake we are using a type with 3 milliseconds precision. The loop itself takes less that that to iterate (depending of your server). The key here is internaly that time stamp is a float and the integer type counts how many days passed. It ill work fine in January 1, 1753, through December 31, 9999 date range. # VBA, 258 Bytes ### Ran with:Excel 2007 in Windows 7 305 bytes if Usability is required WARNING This MAY Max your CPU and Crash Excel/Windows if you are on a Single Threaded single core computer (Most likely found in 1985) Sub q() h=CDbl(Now()) While 1 t=CDbl(Now()) If t>h+1 Then Debug.Print (CDate(t) & " " & CDate(h) & ":" & Year(t) & "? You mean we're in the future?") If t<h Then Debug.Print (CDate(t) & " " & CDate(h) & ": Back in good old " & Year(t) & ".") h=t Wend End Sub  If you want this Code to be "Testable" then add Application.Wait (Now() + TimeValue("0:00:01")) after h=t ### Output 10/22/2015 3:04:45 PM 10/22/2015 3:04:43 PM:2015?You mean we're in the future? 10/22/2015 3:06:48 PM 10/22/2015 3:06:46 PM: Back in good old 2015.  Below is the test file I used. I'm Honestly Amazed at how little security Windows has sometimes. May not run as expected on all computers Run at Own Risk Could Have Major lasting Side Effects!!!! Sub DOC() t = 31346.6868055556 Date = DateSerial(Year(t), Month(t), Day(t)) Time = TimeSerial(Hour(t), Minute(t), Second(t)) q End Sub  # C: 363 bytes Minified using this handy script: #include<stdio.h> #include<time.h> void p(time_t*t){char b[64];strftime(b,64,"%FT%T",localtime(t));printf("%s ",b);}int main(void){time_t a,b,d=60*60*24;int y;time(&a);while(1){time(&b);y=localtime(&b)->tm_year+1900;if(b<a){p(&a);p(&b);printf("Back in good old %d\n",y);}else if(b>a+d){p(&a);p(&b);printf("%d? You mean we're in the future?\n",y);}a=b;sleep(1);}}  Original: #include <stdio.h> #include <time.h> void p(time_t * t) { char b[64]; strftime(b, 64, "%FT%T", localtime(t)); printf("%s ", b); } int main(void) { time_t a, b, d = 60*60*24; int y; time(&a); while(1) { time(&b); y = localtime(&b)->tm_year+1900; if (b < a) { p(&a); p(&b); printf("Back in good old %d\n", y); } else if (b > a + d) { p(&a); p(&b); printf("%d? You mean we're in the future?\n", y); } a = b; sleep(1); } }  Example run: 2015-10-23T23:30:03 1985-06-14T16:27:00 Back in good old 1985 1985-06-14T16:27:07 1999-02-09T14:15:00 1999? You mean we're in the future? 1999-02-09T14:15:09 2015-02-09T14:15:00 2015? You mean we're in the future? 2015-02-09T14:15:36 2015-10-21T07:28:00 2015? You mean we're in the future? 2015-10-21T07:29:06 1985-10-26T09:00:00 Back in good old 1985 1985-10-26T09:00:28 2055-11-12T06:38:00 2055? You mean we're in the future? 2055-11-12T06:38:12 1919-10-07T00:09:57 Back in good old 1919 1919-10-07T00:09:57 2055-11-12T06:38:14 2055? You mean we're in the future? # tried to go to 1955 - fail. 2055-11-12T06:39:09 2015-10-23T23:32:03 Back in good old 2015 # auto-time back to 2015 because my laptop didn't like the jump to 2055!  I could get rid of 10 bytes by removing the sleep I guess. By the way, some time-jumping handiness for Mac/Linux: sudo date 1026090085 # Sat 26 Oct 1985 09:00:00 sudo date 1021072815 # Wed 21 Oct 2015 07:28:00 sudo date 1112063855 # Intended to be 1955 but is 2055. Don't use!  • Feel free to drop the sleep. Oct 25 '15 at 7:49 # JavaScript (ES6) 181174 170 Bytes for(a=Date;c=b||a.now(),b=d();e=new a(b).getFullYear(),f=${a(c)} ${a(b):})b>c+864e5?(g=alert)${f} ${e}? You mean we're in the future?:c>b&&g${f} Back in good old +e

Note: Has not been tested with a real time machine.

This code runs in Firefox, Chrome, Edge, Node.js Harmony (or io.js for that matter). But, I use alert, so that will have to be replaced by console.log for Node and Io Suport: (187 Bytes)

for(a=Date,b=0;c=b||(d=a.now)(),b=d();e=new a(b).getFullYear(),f=${a(c)}${a(b):})b>c+864e5?(g=console.log)${f}${e}? You mean we're in the future?:c>b&&g${f} Back in good old${e}.

Explained:

// Using for like a while loop, defining relevant variables:
for (a = Date, b = 0;
// Defing b and c: c becomes b, b becomes now. Also defining a shorthand for Date.now:
c = b || a.now(),
b = d();
// Defining Variables Relevant to this loop: e is the year according to b, f is the "TS TS:" string:
e = new a(b).getFullYear(),
f = ${a(c)}${a(b):
)
// If b is greater than c plus a day (in milliseconds):
b > c + 864e5 ?
${f}${e}? You mean we're in the future?:
// else if c is greater than b:
c > b &&
g ${f} Back in good old +e  • I managed to write an even shorter one, you might want to have a look at it and possibly make yours better. Also, I think it is great! Oct 23 '15 at 13:34 • How big was your solution, I want to see if I can beat it? ;) – bren Oct 24 '15 at 3:57 • Scroll down or click on the link: codegolf.stackexchange.com/a/61544/33160 Also, you are pretty close to beating it! :D Oct 24 '15 at 7:40 ## Processing, 270 bytes int p;long x=System.currentTimeMillis();void draw(){int q=millis(),y=year();if(q<p){t(p);print("Back in good old "+y+".");}if(q>p+86400000){t(p);print(y+"? You mean we're in the future?");}p=q;}void t(int m){print(new java.util.Date(x+m)+" "+new java.util.Date()+": ");}  Expanded: int p; long x=System.currentTimeMillis(); void draw() { int q=millis(), y=year(); if (q<p) { t(p); print("Back in good old "+y+"."); } if (q>p+86400000) { t(p); print(y+"? You mean we're in the future?"); } p=q; } void t(int m) { print(new java.util.Date(x+m)+" "+new java.util.Date()+": "); }  Sample output: Wed Oct 21 13:21:59 EDT 2015 Mon Oct 19 13:21:59 EDT 2015: Back in good old 2015. Mon Oct 19 13:22:08 EDT 2015 Wed Oct 21 13:22:08 EDT 2015: 2015? You mean we're in the future  # Ruby, 160157155 154 bytes A lot of things to golf here a=Time.new;loop{b,s,y=Time.new,"#{a} #{b}: ",b.year;$><<(a>b ? s+"Back in good old #{y}.\n":b>a+86400 ? s+"#{y}? You mean we're in the future?\n":"");a=b}

# Mathematica, 295 bytes

The program asks the OS every second for new TS.

f:=LocalTime[]
p=Print;
y:=DateString[#,"Year"]&
s:=ToString[#]<>" "&
d:=QuantityMagnitude@DateDifference[a,b]
j=StringJoin;
While[True,
a=b;
b=f;
Pause@1;
Which[d>=0,
p@(j@@{s@a,s@b,": ",y@b,
"? You mean we are in the future?"}),
d<0,
p@(j@@{s@a,s@b," Back in good old ",y@b,"."})]];

# Output

Tested by manually feeding in date/time.

DateObject[{2015, 10, 23}, TimeObject[{18, 36, 17.9618}], TimeZone -> \
-4.] DateObject[{2015, 10, 25}, TimeObject[{18, 42, 0.264913}], \
TimeZone -> -4.] : 2015? You mean we are in the future?

DateObject[{2015, 10, 23}, TimeObject[{18, 43, 0.141572}], TimeZone -> -4.] DateObject[{2015, 10, 23}, TimeObject[{18, 42, 3.30681}], TimeZone -> -4.]  Back in good old 2015.

Definitely could have format the output better. It does fulfill the requirements as stated.

• why do you shortcut LocalTime[]? It appears only once in the following code. Oct 30 '15 at 15:18
• At one point, I was using it twice. Good catch though. Oct 30 '15 at 16:45
• Remove it and you save three characters. Oct 30 '15 at 16:54

# Javascript 173 169 162 bytes

Javascript is pretty popular...

for(e=Date,n=e.now;o=n(a=alert);)d=new e,f=d.getFullYear(n(o>n(s=d+ ${e(o)}:)&&a(s+Back in good old${f}.))-o>864e5&&a(s+f+? You mean we're in the future?))

Explanation (Older version of the code):

for(e=Date,n=e.now,a=alert,o=n();;o=n()) //Set up the variables and update o, the previous time

d=new e,s=d+ ${e(o)} ,f=d.getFullYear(), //d is the date, s is a string with the 2 timestamps, f is the year n()-o>8.64e7&&a(s+f+? You mean we're in the future?), //Future check o>n()&&a(s+Back in good old${f}.) //Past check

# Groovy, 244 bytes

def s=9999,d={new Date()},y={it.year+1900},f={t,n->"$t$n: ${y(n)}? You mean we're in the future?"},p={t,n->"$t $n: Back in good old${y(n)}."},t=d()
while(!sleep(s)){n=d()
c=n.time-t.time
println c<0?p(t,n):c>s*2?f(t,n):'Great Scott!'
t=n}


text:
# A general solution to continuity equation

Let us write the standard continuity equation $$\frac{\partial \rho}{\partial t} + \vec{\nabla} \cdot \vec{\jmath} = 0.$$

Should the relation $\vec{\jmath} = \rho \vec{v}$ be considered as a general solution of the continuity equation? If so, how to derive it?

• $\vec j=\rho \vec v$ is not a solution of the continuity equation, it is a parametrization of the variables present in it. With just this continuity equation, you can't get any solution because you have 1 (scalar) equation and 4 indepent variables. – Hydro Guy May 4 '14 at 19:44
• Generally one numerically solves this problem. If you have strict boundary conditions and initial conditions, it may be possible to analytically solve for $\rho$. – Kyle Kanos May 4 '14 at 21:17
• I was thinking more along the lines of... The general solution of the wave equation in 1D is of the form $f(x \pm ct)$, with $f$ arbitrary. – user17116 May 4 '14 at 22:25

format: plain


text:
By accessing our 180 Days of Math for Sixth Grade Answers Key Day 72 regularly, students can get better problem-solving skills.

Directions Solve each problem.

Question 1.
75 + 68 = ____

Question 2.
-10 × 15 = _____
– ×  + = –
-10 × 15 = -150

Question 3.

Answer: 276 ÷ 7 = 39.4

Question 4.
Write 86,391 in expanded notation.
____________
____________
86,391 in expanded notation is 80,000 + 6,000 + 300 + 90 + 1

Question 5.
How many tenths are in 2$$\frac{2}{10}$$?
_______________________
2$$\frac{2}{10}$$ = $$\frac{22}{10}$$
There are 22 tenths in 2$$\frac{2}{10}$$.

Question 6.
9 + (-50) + 70 = ______
9 – 50 + 70 = 29

Question 7.
Solve for g. $$\frac{1}{3}$$g = 12
g = ____
Given,
$$\frac{1}{3}$$g = 12
g = 12 × 3
g = 36

Question 8.
$$\frac{4}{5}$$ of = 24
Let the unknown value be x.
$$\frac{4}{5}$$ × x = 24
x = 24 × 5/4
x = 6 × 5 (24 divided by 4 is 6)
x = 30

Question 9.
How many grams are in 2.525 kilograms?
_______________________
Convert from kilograms to grams.
1 kg = 1000 grams
2 kgs = 2000 grams
2.525 = 2525 grams

Question 10.
Name the two quadrilaterals with four equal sides.
_______________________
_______________________
Square and Rhombus

Question 11.
What is the probability you will spin a word that has two letters that are the same in it?
_______________________


text:
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# As a salesperson, Phyllis can choose one of two methods of a

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The Official Guide For GMAT® Quantitative Review, 2ND Edition

As a salesperson, Phyllis can choose one of two methods of annual payment: either an annual salary of $35,000 with no commission or an annual salary of$10,000 plus a 20 percent commission on her total annual sales. What must her total annual sales be to give her the same annual pay with either method?

(A) $100,000 (B)$120,000
(C) $125,000 (D)$130,000
(E) $132,000 Problem Solving Question: 127 Category: Algebra Applied problems Page: 78 Difficulty: 600 GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition - Quantitative Questions Project Each week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution. We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button; 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation. Thank you! [Reveal] Spoiler: OA _________________ Math Expert Joined: 02 Sep 2009 Posts: 44421 Re: As a salesperson, Phyllis can choose one of two methods of a [#permalink] ### Show Tags 05 Mar 2014, 02:06 SOLUTION As a salesperson, Phyllis can choose one of two methods of annual payment: either an annual salary of$35,000 with no commission or an annual salary of $10,000 plus a 20 percent commission on her total annual sales. What must her total annual sales be to give her the same annual pay with either method? (A)$100,000
(B) $120,000 (C)$125,000
(D) $130,000 (E)$132,000

35,000 = 10,000 + 0.2*x --> x = 125,000.

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Re: As a salesperson, Phyllis can choose one of two methods of a [#permalink]

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05 Mar 2014, 20:48
2
KUDOS
Answer = (C) $125,000 35000 = 10000 + 25000 We require to calculate sales which creates a commission of 25000 @ 20% = $$25000* \frac{100}{20}= 125000$$ _________________ Kindly press "+1 Kudos" to appreciate Manager Status: GMATting Joined: 21 Mar 2011 Posts: 108 Concentration: Strategy, Technology GMAT 1: 590 Q45 V27 Re: As a salesperson, Phyllis can choose one of two methods of a [#permalink] ### Show Tags 05 Mar 2014, 21:15 2 This post received KUDOS 1st method of annual payment = 35,000 + no commission = 35,000 2nd method of annual payment = 10,000 + 1/5TS, where TS is Total Sales Since the annual pay is the same, as per the question, we can equate the 2 equations: 35,000 = 10,000 + 1/5 TS 1/5 TS = 25,000 TS = 125,000 Ans is (C) Intern Joined: 03 Aug 2012 Posts: 20 Location: United States (OR) Concentration: Finance, International Business GPA: 3.53 WE: Analyst (Entertainment and Sports) Re: As a salesperson, Phyllis can choose one of two methods of a [#permalink] ### Show Tags 05 Mar 2014, 22:58 1 This post received KUDOS Option #1: Annual Salary (A) =$35,000

Option #2:

Annual Salary (A) = $10,000 + .2 * Total Sales (S) Solution: Step 1 -->$35,000 = $10,000 + (1/5)S Step 2 -->$25,000 = (1/5)S
Step 3 --> $25,000(5/1) = S Step 4 -->$125,000 = S

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Posts: 44421
Re: As a salesperson, Phyllis can choose one of two methods of a [#permalink]

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08 Mar 2014, 12:14
SOLUTION

As a salesperson, Phyllis can choose one of two methods of annual payment: either an annual salary of $35,000 with no commission or an annual salary of$10,000 plus a 20 percent commission on her total annual sales. What must her total annual sales be to give her the same annual pay with either method?

(A) $100,000 (B)$120,000
(C) $125,000 (D)$130,000
(E) $132,000 35,000 = 10,000 + 0.2*x --> x = 125,000. Answer: C. _________________ Manager Joined: 05 Jul 2015 Posts: 106 Concentration: Real Estate, International Business GMAT 1: 600 Q33 V40 GPA: 3.3 Re: As a salesperson, Phyllis can choose one of two methods of a [#permalink] ### Show Tags 22 Nov 2015, 10:39 Took me 45 seconds total. 35=10+(1/5)X 25*5 = 125 EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 11312 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: 340 Q170 V170 Re: As a salesperson, Phyllis can choose one of two methods of a [#permalink] ### Show Tags 25 Nov 2015, 15:51 Hi All, This question can be solved by TESTing THE ANSWERS. From the information in the prompt, we're looking for a sales total that, when we take 20% of it, gives us$25,000. While this can be solved algebraically, we do have 5 answer choices to use as reference.

If Sales = $120,000 20% of$120,000 = (1/5)(120,000) = 24,000
This is remarkably close, but it's just a little TOO SMALL...

If Sales = $125,000 20% of$125,000 = (1/5)(125,000) = 25,000
This is an exact MATCH for what we were looking for, so this MUST be the answer.

[Reveal] Spoiler:
C

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Special Offer: Save $75 + GMAT Club Tests Free Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/ ***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*********************** Intern Joined: 20 Oct 2015 Posts: 43 Re: As a salesperson, Phyllis can choose one of two methods of a [#permalink] ### Show Tags 05 Jul 2016, 07:12 [quote="Bunuel"]The Official Guide For GMAT® Quantitative Review, 2ND Edition As a salesperson, Phyllis can choose one of two methods of annual payment: either an annual salary of$35,000 with no commission or an annual salary of $10,000 plus a 20 percent commission on her total annual sales. What must her total annual sales be to give her the same annual pay with either method? (A)$100,000
(B) $120,000 (C)$125,000
(D) $130,000 (E)$132,000

35000-10000=25000

25000=20% * x

x=25000 / 20% = 125000
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Re: As a salesperson, Phyllis can choose one of two methods of a [#permalink]

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16 Jul 2017, 17:46
1
KUDOS
Expert's post
Bunuel wrote:

As a salesperson, Phyllis can choose one of two methods of annual payment: either an annual salary of $35,000 with no commission or an annual salary of$10,000 plus a 20 percent commission on her total annual sales. What must her total annual sales be to give her the same annual pay with either method?

(A) $100,000 (B)$120,000
(C) $125,000 (D)$130,000
(E) $132,000 We can let total annual sales = x and create the following equation: 35,000 = 10,000 + 0.2x 25,000 = 0.2x 125,000 = x Answer: C _________________ Scott Woodbury-Stewart Founder and CEO GMAT Quant Self-Study Course 500+ lessons 3000+ practice problems 800+ HD solutions Manager Joined: 21 Jun 2017 Posts: 78 As a salesperson, Phyllis can choose one of two methods of a [#permalink] ### Show Tags 24 Aug 2017, 01:34 Let X = Annual Sales 1.$10,000 + (.2 * X) = $35,000 2. .2x =$25,000
3. x = \$125,000

As a salesperson, Phyllis can choose one of two methods of a   [#permalink] 24 Aug 2017, 01:34
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text:
# days between dates

Seems like finding out days between dates is not a trivial task. There is quite a bit of support in tools for adding up dates (date), but literally none for evaluating the difference. Unix systems return time using epoch as reference, thus you need to divide the difference by 86400 (#seconds in a day) to get the #days. However I wanted something portable that would work across all platforms without me having to worry about leap-years and such esoteric stuff.

The obvious choice then became python (a bit more readable compared to shell scripts). Anyway here is the python script to give you the days between dates using date object:

 1 2 3 4 5 6 7  from datetime import date # add 1 to account for today as well # 1982 days ago I started my blog (first post on 4 Jan 2009) # Note: do not to add 0 in front of 1 or 4 (Month or Day) # seems like python hates it that way.. # (date.today() - date(2009, 1, 4)).days + 1


text:
## Beagle, Computing in Science and Engineering

From: "andrew cooke" <andrew@...>

Date: Wed, 24 Dec 2008 11:05:23 -0300 (CLST)

While at the AGU conference I noticed this magazine (Computing in Science
and Engineering) - http://cise.aip.org/

It's not the most professional looking magazine in the world, but it is by
far the closest I've found to a magazine that covers the kind of work I
do.  So I subscribed - got a cheap price and the last 10 years on CD.

I copied the back issues from CD to my hard drive and then wondered what
to do.  They are broken down into one article per file, but they are PDF
and I had no way of searching them.

Then I remembered Beagle, which I have carefully de-installed from my
computer for several years now because it seemed (1) useless and (2) used
up so much CPU.  Beagle is the default Linux document indexing system

Anyway, it's improved hugely.  It no longer locks up the computer when
you're trying to get something done.  And it appears to return moderately
useful results.  So I can now search for something like "python numerical
vector" and the second hit (when ordered by relevance) is "Python for
Scientific Computing" from the magazine.

You can also restrict to certain file types (ext:pdf), exclude terms
(-foo), etc etc.  It even indexes music metadata (so you can search for
artists) and email.

The KDE Kerry interface does quite a good job of presenting the data too -
you can click on a file and it is handed off to an appropriate handler
(although HTML is going to konquerer instead of the mozilla configured for
the desktop).

It does, however, still seem to crash quite regularly.  You can see this
by doing

tail ~/.beagle/Log/current-Beagle

which will show a message about SIGSEGV or by typing beagle-status which
will say it cannot connect.  To restart just type "beagled" at the command
line.

I also enabled extended filesystem attributes by modifying the fstab from
/home to include the user_xattr option.  Apparently this makes things a
bit faster.

One check I did, when I found some old files I thought I had been deleted,
surprised me: it immediately picks up on deleted files and excludes them
from the results.  Which is nice.

Andrew

### Tweaking Beagle and KDE

From: "andrew cooke" <andrew@...>

Date: Wed, 31 Dec 2008 12:32:28 -0300 (CLST)

While Kerry (the KDE Beagle client) looks nicer (more compact), it hangs
regularly.  The Beagle search app (beagle-search from the command line, or
just "Search" from the SuSE menu) is much more robust.

If you use Firefox, you need to make sure that:

1 - the default browser is Firefox.  Configure Desktop -> General ->
Default Applications -> Web Browser

2 - html files are associated with Firefox.  Configure Desktop -> Advanced
-> File Associations and then find text/html in the tree widget.

To make sure that everything is indexed at the start, follow the
instructions at http://beagle-project.org/FAQ

$beagle-shutdown$ export BEAGLE_EXERCISE_THE_DOG=1
\$ beagled

Also enable user attributes on your file system by modifying /etc/fstab as
described at http://beagle-project.org/Enabling_Extended_Attributes

To check what is happening, use beagle-status, but don't be worried if
there are a lot of directories to scan on subsequent logins.  Each login,
beagle slowly re-scans everything.

To check whether a particular file is indexed, use
beagle-query uri:file:///path/to/file
and see fi anything is returned.

I still haven't worked out how to get email indexed.  I use imap, and have
the files downloaded locally, but I don't use kmail or evolution and the
files are generally in directories whose names begin with a "dot".  I
think you can fake things by configuring kmail or evolution (in addition
to the email client you actually use), but this still doesn't track any
changes.  The file backend will handle emails, but doesn't look in "dot"
files.  Apparently symlinks don't fool it either...

Andrew


text:
# Understanding a proof of the vanishing of the Weyl tensor for a diagonal Riemannian metric

I'm currently working through this paper from Duke Math J., Volume 51, Number 2 (1984), 243-260 (unfortunately couldn't find a publicly visible link); more specifically, the part about the obstructions to the diagonalizability of Riemannian metrics in $$n \geq 4$$ dimensions, but there are a few parts where I just can't wrap my head around what's happening.

On page 258, they start by taking an orthonormal coframe $$\{\omega^i = f^i d x^i : i = 1, ..., n\}$$ altogether with it's dual frame $$\{e_i\}$$. Their goal is to show that the Weyl-tensor $$W$$ vanishes, so that one can apply the Weyl-Schouten theorem to get that the manifold is already conformally flat.

Using some calculations with the connection form $$\omega_j^i$$ and Cartan's structure equations which I can for the most part follow, they arive at the result that

$$d(\omega^i \wedge \omega^j \wedge \omega_j^i) = \omega^i \wedge \omega^j \wedge \Omega_j^i = 0 \text{ for } i \neq j$$

where $$\Omega_j^i$$ is the curvature $$2$$-form.

Now from this, Deturck and Yang make the jump to the sectional curvature $$R$$ and then on to the Weyl Tensor $$W$$. Namely, they argue the following:

Thus $$\omega^i \wedge \omega^j \wedge \Omega_j^i = 0$$ for all $$i \neq j$$. This will manifest itself as an integrability condition, as we shal see. Rewriting this in terms of the sectional curvature $$R$$, we must have

$$R(e_i, e_j, e_k, e_l) = 0 \text{ if i, j, k, l are distinct}$$

where $$\{e_i\}$$ is the dual frame to $$\{\omega^i\}$$.

How do they make this jump? How can we come from the equation $$\omega^i \wedge \omega^j \wedge \Omega_j^i = 0$$ where we have only two distinct components $$i, j$$ to the equation with four distinct components $$i, j, k, l$$ for which the curvature $$R$$ vanishes? What exactly do we do when "rewriting" this equation, as they only call it? It might be due to my limited experience with these things, but I fail to see the exact relation between the first equation and the vanishing of the curvature tensor for these four components.

Right thereafter, they continue to carry over this equation about the Weyl tensor, namely

Since $$\{e_i\}$$ is an orthonormale frame, none of these components of $$R$$ enter into the Ricci tensor. We conclude that

$$W(e_i, e_j, e_k, e_l) = 0 \text{ if i, j, k, l are distinct}$$

where $$W$$ is the Weyl tensor.

This seems less obscure to me, but I don't understand it entirely either. My first question would be, how do we get from the $$\{e_i\}$$ being orthonormal to not entering into the Ricci tensor? Is this some property of the Ricci-tensor that I'm missing?

And my 2nd question here would be: I know that the Riemannian curvature tensor decomposes into the "trace"-part (Ricci-Tensor) and the "traceless"-part (Weyl-Tensor). Is this the argument Deturck and Yang use here to conclude the $$W(...) = 0$$-equation? That if the components don't enter into the Ricci-tensor, they can only be in the only other part the curvature tensor consists of, namely the Weyl-tensor, so if one of them is $$= 0$$, the other one is too? Am I understanding this argument correctly? (Even if I probably didn't express it too well...)

From there on, they continue with some calculations that I can roughly follow to show that $$W \equiv 0$$, but I just can't wrap my head around about this passage. I haven't worked that much with Weyl- and Curvature tensors before, so maybe some stuff I have trouble with has a very easy explanation that I'm just missing out on. Any help would be greatly appreciated.

• This paper sounds interesting. Can you please say where can I find it on the web? I have trouble locating it. Aug 18 '17 at 19:12
• @AsafShachar Unfortunately I couldn't find any publicly available web location of it myself, otherwise I would have happily linked it. I've added a link in the post where the document can be bought from. I hope this is of help to you. Aug 18 '17 at 21:13

I suppose the sectional curvature $R$ actually means Riemann curvature instead, since sectional curvatures are usually defined on planes in tangent spaces intead of on $\ts^4T_xM .$
First note that $\om^i\w\om^j\w \Om^i_j$ is a $4$-form, and this is where the four inputs $i,j,k,l$ come from. By the shuffle definition of wedge product, we have $$\om^i\w\om^j(e_m,e_n)=\om^i(e_m)\om^j(e_n)-\om^i(e_n)\om^j(e_m)=\e^{ij}_{mn},$$ where $\e^{ij}_{mn}=1$ when $(m,n)=(i,j),$ $-1$ when $(m,n)=(j,i),$ and $0$ otherwise.
We know that $\Om^i_j(X,Y)=-R(X,Y,e_i,e_j),$ so for $i,j,k,l$ distinct we have \begin{align*} 0=-&\om^i\w\om^j\w \Om^i_j(e_i,e_j,e_k,e_l)\\=&\sum_{\si\in Sh_{2,2}}(-1)^\si\om^i\w\om^j(e_{\si(i)},e_{\si(j)})R(e_{\si(k)},e_{\si(l)},e_i,e_j)\\ =&R(e_k,e_l,e_i,e_j)\\ =&R(e_i,e_j,e_k,e_l), \end{align*} where $Sh_{2,2}$ means $(2,2)$ shuffles, i.e., $\si(i)<\si(j),\si(k)<\si(l).$ $\newcommand{\np}{\wedge\!\!\!\!\!\!\bigcirc}$ Now, we have \begin{align*} W=R-\frac{1}{n-2}(Ric-\frac{S}{n}g)\wedge\!\!\!\!\!\!\bigcirc g-\frac{S}{2(n-2)}g\np g. \end{align*} By definition of Kulkarni-Nomizu product $\wedge\!\!\!\!\!\!\bigcirc,$ we have $T\np g(e_i,e_j,e_k,e_l)=0$ for any 2-tensor $T$ and distinct $i,j,k,l.$ This yields the desired result $$W(e_i,e_j,e_k,e_l)=0.$$
• Thank you! If I may ask, is the fact that $\Omega^i_j(X,Y)=-R(X,Y,e_i,e_j)$ a well-known property? If so, can you please give a short insight into it, or link or refer to a source where I might read up about that? As I didn't know about this relation between the two. Aug 20 '17 at 0:51
• Also, about the part: By definition of Kulkarni-Nomizu product $\wedge\!\!\!\!\!\!\bigcirc,$ we have $T\np g(e_i,e_j,e_k,e_l)=0$ for any 2-tensor $T$ and distinct $i,j,k,l.$ If I'm understanding this right, this is because the $\{e_i\}$ are an orthonormal frame, so all the $g(e_i, e_j)$ in the definition of the Kulkarni-Nomizu product are $= 0$ for $i \neq j$? Aug 20 '17 at 0:54
• @moran, for the first question, the identity follows from expanding the covariant derivative definition of Riemann curvature using moving frame forms. Please refer to Chapter 1.8 in Riemannian Geometry by Issac Chavel. For the second question, yes. If we follow the sign convention on wikipedia, then $(h {~\wedge\!\!\!\!\!\!\bigcirc~} k)(X_1,X_2,X_3,X_4) := h(X_1,X_3)k(X_2,X_4) + h(X_2,X_4)k(X_1,X_3) - h(X_1,X_4)k(X_2,X_3) - h(X_2,X_3)k(X_1,X_4) .$ Aug 20 '17 at 1:34


text:
# Iguana Tries To Eat Andrew Loupe's Ball At Puerto Rico Open (VIDEO)

With only two holes to go at the Puerto Rico Open, Andrew Loupe probably thought he’d seen everything. And then this happened.

While his ball was laying on the green at the 16th hole, a scaly intruder came out of the brush and made his move. After taking a few chomps at the ball, the PGA Tour’s first iguana putter ran back to the wilderness.

Loupe would par the hole and finish tied for 12th at the tournament.

WATCH VIDEO ABOVE


text:
United States Department of Labor

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## Current Employment Statistics - National: Design

The Current Employment Statistics (CES) sample is a stratified, simple random sample of worksites, clustered by unemployment insurance (UI) account number. The UI account number is an identifier on the Bureau of Labor Statistics (BLS) longitudinal database (LDB) of employer records, which serves as the sampling frame for CES employment estimates. The sample strata, or subpopulations, are defined by state, industry, and employment size, yielding a state-based design. Sampling rates for each stratum are determined through a method known as optimum allocation, which distributes a fixed number of sample units across a set of strata to minimize the overall variance, or sampling error, on the primary estimate of interest. The total nonfarm employment level is the primary estimate of interest, and the CES sample design gives top priority to measuring it as precisely as possible or minimizing the statistical error around the statewide total nonfarm employment estimates. The CES-State and Area (CES-SA) program uses the same sample and collection methods, thus references to CES apply to both CES-N and CES-SA programs.

### Frame and sample selection

The longitudinal database (LDB) of employer records is the universe from which CES draws the establishment survey sample. The LDB contains data on roughly 10.7 million business establishments and state and local governments covered by UI and representing nearly all elements of the U.S. economy. The Quarterly Census of Employment and Wages (QCEW) program collects these data from employers on a quarterly basis in cooperation with labor market information agencies (LMIs). The LDB, which is made from the QCEW, contains employment and wage information from employers, as well as name, address, and location information. It also contains identification information such as UI account number and reporting unit or worksite numbers.

The LDB contains records of all employers covered under the UI tax system in each state and covers about 97 percent of all employment within the scope of CES. With UI laws that can vary by state, some types of workers are not covered by UI, and are not counted by the QCEW. Some, but not all, noncovered workers are within the scope of CES. For example, CES includes employees of railroads and religious organizations, elected officials, and student workers, who are typically not covered by UI. Data for employers generally are reported at the worksite level. Employers with multiple establishments within a state usually report data for each worksite. The LDB tracks establishments over time and links them from quarter to quarter.

The total private and government portions of the CES sample are selected using two different methods. Private establishments in the CES sample frame are stratified by state, industry, and size. Stratification groups population members together for the purpose of sample allocation and selection. The strata, or groups, are composed of homogeneous units, with 13 industries (mining and logging, construction, manufacturing, wholesale trade, retail trade, transportation and warehousing, utilities, information, financial activities, professional and business services, private education and health services, leisure and hospitality, and other services) and 8 size classes, resulting in 104 allocation cells per state. (See exhibit 1.)

Exhibit 1. Employment by class code
Size Class Number of employees

1

0–9 employees

2

10–19 employees

3

20–49 employees

4

50–99 employees

5

100–249 employees

6

250–499 employees

7

500–999 employees

8

1000+ employees

The sampling rate for each stratum is determined through a method known as optimum allocation. Optimum allocation minimizes variance at a fixed cost or minimizes cost for a fixed variance. Under the CES probability design, a fixed number of sample units for each state is distributed across the allocation strata in such a way as to minimize the overall variance, or sampling error, of the over-the-month change for total state employment. The number of sample units in the CES probability sample are fixed according to available program resources and are reviewed and updated every 5 years to realign survey resources with employment changes in each state, while maintaining a certain level of accuracy in each state. The optimum allocation formula, using Neyman’s allocation, places additional sample in strata with greater variance and more units.

Some units, called certainty units, are always asked to be a part of the sample. These units, assigned weight of 1 to represent only themselves, must meet at least one of the following conditions:

• UI accounts in size class 8
• UI accounts in size class 7, which have declined in size from class 8
• Units that provide their information via Electronic Data Interchange (EDI)
• Noncovered employment units that are not covered under the UI system

The CES government sample is not part of the program's probability-based design. CES is able to achieve a very high level of universe employment coverage in government by obtaining full payroll employment counts for many government agencies, eliminating the need for a probability-based sample design. Government estimates are summed with the total private estimates to obtain estimates of total nonfarm employment.

Updated universe files provide the most recent information about industry, size, and metropolitan area designation. The CES program draws a sample each year from the first quarter LDB data when it becomes available later in the year. Annual sample selection helps keep the CES survey current with respect to employment from business births and business deaths. An additional birth update is drawn from the third quarter LDB when it becomes available the next year.

The sampling frame is separated into allocation cells after all out-of-scope records are removed. Units in each allocation cell are grouped by metropolitan statistical area (MSA) sorted by the number of UI accounts in each MSA. As the sampling rate is uniform across the entire allocation cell, implicit stratification by MSA ensures that a proportional number of units are sampled from each MSA. Some MSAs may have too few UI accounts in the allocation cell; these MSAs are combined and treated as a single MSA.

Permanent random numbers (PRNs) are assigned to all UI accounts on the sampling frame. As new units appear on the frame, random numbers also are assigned to those units through a process called collocation. The PRN carries forward as records are linked across time. All units within each selection cell are sorted by PRN and are selected according to the specified sample selection rate. The number of units selected randomly from each selection cell is equal to the product of the sample selection rate and the number of eligible units in the cell plus any carryover from the prior selection cell. The result is rounded to the nearest whole number. Carryover is defined as the amount that is rounded up or down to the nearest whole number.

Collocation of new birth units occurs every quarter with the update of the CES frame. CES assigns each birth unit a random number and then ranks each unit within each stratum by that random number. The following formula ensures that the new units have equal distances between each other within a strata in an order based on their rank, shown in equation 1.

###### Equation 1. Birth sample selection

$PRN hi = R hi - ε h / N h$

where,

$h = stratum indicator;$
$i= a unit within stratum h;$
$R hi = rank of birth unit within stratum h ;$
$N h = number of new birth records to collocate in stratum h ;and$
$ε h = r andom number from the uniform 0,1 distribution.$

All units remain in the sample for a minimum of 2 years because of the added cost and workload associated with enrolling new sample units. A "swapping" procedure ensures that all units meet this minimum requirement. The procedure allows units to be swapped into the sample that were newly selected during the previous sample year and not reselected as part of the current probability sample. The procedure removes a unit within the same selection cell and places the newly selected unit from the previous year back into the sample. To reduce respondent burden, a similar procedure swap units out of the sample that have been sample members for 4 or more consecutive years. The swap-out procedure removes an established sample unit from its selection cell and replaces it with a new unit in the same selection cell. In order to maintain an implicit, proportional allocation across MSAs in the same strata, the ideal unit swap would occur within the same stratum and MSA. On rare occasions, a swap may involve a unit from a different MSA, but the stratum must remain the same. If a unit has been identified for swapping, and there are no units available in the same stratum, then the swap will not take place. Approximately 66 percent of the CES sample for private industries overlaps from the previous sample to the current sample.

### Selection weights

Once the sample is drawn, sample selection weights are calculated based on the number of UI accounts actually selected within each allocation cell. The sample selection weight is approximately equal to the inverse of the probability of selection, or the inverse of the sampling rate, shown in equation 1.

###### Equation 2. Sample selection weights

$Sample selection weight = N h / n h$

where,

$N h = n umber of noncertainty UI accounts in the allocation cell eligible for sample selection; and$
$n h = number of noncertainty UI accounts selected in the allocation cell.$

#### Reweighting

Sample units that are reporting for anything other than the sample unit are reviewed for reweighting. This can happen when a unit merges with another UI account after the sample selection. If two units, A and B, are from different strata, CES uses the following formula to assign the merged weight.

Equation 3. Reweighting

$Newweight = W B W A W B + W A - 1$

where,

$W A = selection weight of unit A;and$
$W B = selection weight of unit B.$

The weight is designed to always be the inverse of the probability of selection, but when the two units are from the same strata, their probability of selection is dependent on the other unit being selected. The general formula is below:

$Newweight = 1 P A + P B - P A and B$

where,

$A = probability of selecting unit A ;$
$P B = probability of selecting unit B;and$
$P A and B = probability of selecting unit A and B.$

### Frame maintenance and sample updates

Because of the dynamic nature of the economy, there is a constant cycle of business openings (births) and closings (deaths). A sample update is performed during the summer each year, drawing from the previous year's third quarter LDB data. This update selects units from the population of openings and other units not previously eligible for selection and includes them as part of the sample. Location, contact, and administrative information are updated for all establishments that were selected as part of the sample updates.

### Coverage

Table 1, available at https://www.bls.gov/web/empsit/cestn.htm#tb1, shows March 2021 benchmark employment levels for total nonfarm and major industry sectors and the approximate proportion of total universe employment coverage. The coverage for individual industries within each sector may vary from the proportions shown.

#### CES sample by private-sector industry

The CES program uses a probability-based sample to estimate employment for all private industries. Sample distribution by industry reflects the goal of minimizing sampling error in total nonfarm employment estimates, while also providing reliable employment estimates by industry. Sample coverage rates vary by industry as a result of building a design to meet these goals. For example, manufacturing had 12.2 million employees in March 2021, while leisure and hospitality had about 12.9 million employees. However, their relative sample sizes differ. Manufacturing has 14,799 sample establishments and about 2.7 million employees, while leisure and hospitality has 67,492 sample establishments and about 2.2 million employees. The manufacturing sample covers about 22 percent of all manufacturing employees in the industry, while the sample for leisure and hospitality covers about 17 percent of all employees in that industry. Some of the difference in each industry’s sample stems from a much larger average firm size in manufacturing. This type of difference does not cause bias in the CES employment estimates, because the use of industry sampling strata and sampling weights ensures that each firm is represented in the estimates.

#### Government sample

The CES program achieves 70 percent universe coverage in its government sample. Consequently, a probability-based sample design is not necessary for government. The coverage rate ensures a high degree of reliability for government employment estimates. Private sector and government employment estimates are summed to get total nonfarm employment. Since the CES program uses government sample to estimate only government estimates, it does not bias the total nonfarm employment estimates.

#### CES sample by employment size class

The employment universe that the CES sample is estimating is highly skewed. (See table 3 at https://www.bls.gov/web/empsit/cestn.htm#tb3.) The largest UI accounts (those with 1,000 employees or more) comprise only 0.2 percent of all UI accounts but contain approximately 29 percent of total private employment. The smallest size class (0–9 employees) contains 72.6 percent of all UIs and about 10.7 percent of total private employment. CES samples larger firms at a higher rate than smaller firms, a standard technique commonly used in business establishment surveys.

A much greater proportion of large UIs are selected for the CES; however, that does not create a bias in either the sample or the estimates. Table 4, available at https://www.bls.gov/web/empsit/cestn.htm#tb4, shows the distribution of the active CES sample units by employment size. Each sample unit selected is assigned a weight based on its probability of selection, ensuring that all firms of its size are properly represented in the estimates. For example, if 1 in every 100 firms are selected from UIs in the smallest firm stratum, they are assigned a weight of 100 because they represent themselves and 99 other firms that were not sampled. The use of sample weights in the estimation process prevents a large- or small-firm bias in the estimates.

Last Modified Date: May 04, 2022


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# MMO Teams everywhere, but not a game to spare.

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## Recommended Posts

It seems that everyone recently (this past couple years) just wants to make MMO's. But the thing is, the more I see these teams, the more I just want to tell them to stop and think. From what I have seen is that they play through a MMO and they say "Hey, I want to make one to" But what they dont realize is that they are jumping in far to deep. Here is the 3 most major errors I seen in people who do just say "I want to make a game" ________________________________________________________________________________ Talent Most of these people have no experience in game development. And yet they beleive they have the ability to become this great person overnight. You need to be able to contribute somehow to have a succesful project. Be it Programming, 3D/2D Art, Music, anything that you can! But as I said before, these people usually have no talent at all in this industry which is a very very hard one to boot. I think that this is needed because your staff will be happy to see that your not just useing them. If you work on it yourself, NO MATTER WHAT THE SIZE OF THE JOB -------------------------------------------------------------------------------- Money OK, So let us assume you have talent in the game design area. Do you have the funds to support a MMO? Because, MMO's are THE hardest thing to pay for there is. Servers, at there least (100MBps, 1GB RAM, 2x Intel Xeon 2.7GHz) are $600 per month. Even to a rich man thats alot of money, hell thats an H2 Hummer right there! I have seen a few cases of people that are allowed to use there schools servers, but they eventually will be kicked off them and have to fend for themselves. -------------------------------------------------------------------------------- Managment Alrighty then, you have talent, and have money...Can you manage the project? As the founder, the staff will look to you for directions. And if you cant point them in the right direction, your team will ultimatly fail. Poor managment is what makes what I would say 80% of these projects end. I even seen a team that were professionals...but there leader was horrible and didnt know that there was actually a programming language called C++....(Kinda sad really, being as he got some professionals on his team and never got to use them) Most managers just say "Go make a red haired guy for me. use your imagination" What they should say is "We need a red haired character, about 5'8'' muscular with blue eyes, here is some concept art as well" And they can not organize things nicely as well....have you ever seen someone just put all there files in ONE folder...I mean ALL THE FILES. Music, Source, Models, Text docs, everything! At least put it in a "Music Folder" "Source Folder" "Model Folder" "Text Folder" layout, rather then just one big lazy pile of files. ________________________________________________________________________________ So now, what can we do to repair this problem? That is the most simplest thing to answer...... START SMALL! No, you dont have to start with a PONG/TETRIS/MARIO clone. You can start with whats called a OneHourGame. Its basicly any genre you want, 2d or 3d. At most it will require 4 people... 2 Programmers, Musician, 3D/2D Artist What you do is make it very cliche' just make it the best design you can possibly make. Story, gameplay, and even art is unneeded. Just design it....DESIGN DESIGN DESIGN. This will give you some of the needed experience to work on something bigger. Each time you make a new game, improve on features you left out in the last one. For example, Game 1: RPG Game 2: RPG w/ better graphics Game 3: RPG w/ better story Game 4: RPG w/ better gameplay Game 5: My First MMORPG Game 6: My Second MMORPG, CLANS! Game 7: My Third MMORPH, Many features!!! Game 8: My Fourth MMORPG, I WILL CHARGE FOR THIS ONE!!! #### Share this post ##### Link to post ##### Share on other sites I have been teaching people C++ for some time now, on msn and the like, and the number of people who ask me to help them make a game when they have little or no knowledge of the language amazes me. But another take on this is that this is the way i began, you don't realise how much hard work it is until you try and make something like this. I have an insane amount of unfinished Visual C++ Solutions on my computer. As you say, designing is SOOO important. Even with the simplest applications it is so easy to start and then think "oh i will add this feature" and instead that feature turns into another solution. I agree with you and disagree at the same time, although alot of people do spend alot of time in making part of an MMO and then not finishing, it is a good learning experience. ace #### Share this post ##### Link to post ##### Share on other sites So so true. I've been learning C++ for about 5 years now, and gmae development for about 1 1/2. A few of my friends want to start a team, one who's been doing BlitzBasic for about a year, and just made a Pong and Galaga clone, and about 6 'designers' (not real designers, just the people who don't know programming or art and just sit there with their thumbs up their asses because they want to make a game). And guess what their first project is? Right, an MMO. Patience spazuhs, patience. </rant> #### Share this post ##### Link to post ##### Share on other sites Quote:  Original post by XisZMoneyOK, So let us assume you have talent in the game design area.Do you have the funds to support a MMO?Because, MMO's are THE hardest thing to pay for there is.Servers, at there least (100MBps, 1GB RAM, 2x Intel Xeon 2.7GHz) are$600 per month.Even to a rich man thats alot of money, hell thats an H2 Hummer right there!

Well, we've been running our game for several years now at a total cost of 0\$ so far. We are using donated servers for both our forums and game server. If you show that you are dedicated to your project and can put together something reasonable there are people out there willing to host your game for you. We've already had people wanting to donate money but we have not looked into that yet.

Quote:
 --------------------------------------------------------------------------------ManagmentAlrighty then, you have talent, and have money...Can you manage the project?As the founder, the staff will look to you for directions.And if you cant point them in the right direction, your team will ultimatly fail.

Yes, this is a pretty good one. You don't need an entire team of experts BUT you do need a core group of people that are experienced in their fields and have them as team leaders. Our team meets once a week on irc to give status reports, discuss what was completed this week and assign out tasks for the next week.

One of the issues I have trouble with is people saying you need a full design document before even starting. That might be good in the industry where you know exactly what you are doing for that design document. But in trying to build an indy team I think people will bail on you if you don't show some actual game progress. After all, it doesn't take a rocket scientist to write down ideas. Now to make them make sense is a totally different issue. Also you need an idea of what is practicle in terms of technology/modeling/implementation. In our system we design around a release, so we come up with a list of features, ideas we want to implement for the next release and repeat. It works out fairly well :)

I think the problems that most of these teams face is that they start off well and have good intentions but after a while they hit a wall. This can be caused by a couple of things like:

1) Missing content ( ie programmer art, crappy models, etc)
2) A major technological block. Something like a fundamental flaw in networking or something screwed up in the GUI system. This is a real biggy because it basically brings progress to a halt.
3) In team fighting. Basically you get more arguements than work done.

The teams that make it are those that can push through these walls. Often time working on the game is great fun but other times it's a total bitch, especially if it something like a major code refactor. But it has to be done some somebody has to step up to the plate :) Keeping things moving forward is the key, even if it's just adding comments or cleaning up code.

I think a big aspect for a team leader is don't assign a task to somebody that you are not willing to give a try yourself ( even if you do suck ) because at some point you may have to be the one to push the game over the wall.

-----------
Andrew

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I think lack of experience is the sole reason why everyone is trying to make a MMORPG. I've learnt how to program, written a few small games, and even worked in the industry, which is why I'm not making a MMORPG; I know enough about the industry to know that I haven't a hope in hell of finishing a MMORPG by myself.

Although it is a bit depressing to see so many new game designers aim for something way beyond their reach. It's not new; back when I was a kid, the cool fad was FPS games like Wolfenstein 3D or Doom. But it actually was possible for a single teenager to make a game like Wolf3D in their spare time. A multimillion dollar graphical MMORPG, however, is not.

I'd understand if they were aiming to make a text based MUD, which is achievable and technically a MMORPG, but that's not the impression of the potential projects that I see in the posts here.

Sorry about the mini-rant. I know I shouldn't really care about it so much, but I just feel a bit sad that so many eager young students in all areas of game cretion are going to fail at their projects due to unrealistic expectations and become disenchanted with game development.

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I agree with the top post. Its sad how many people are hopelessly wasting their time developing MMORPGs that (for the most part) go nowhere when they could be developing games that are fun and have a chance at seeing the light of day. I too, underestimated game programming at first, thinking my 4+ years of "regular" programming was enough. Luckly I was smart enough to avoid the MMORPG trap (I don't really have any interest in them in the first place), but looking back on things, I still think I took too big of a jump initially. Not that it was a bad thing, but I had to learn a lot before I was really able to take my game in the right forward direction.

Quote:
 For example, Game 1: RPGGame 2: RPG w/ better graphicsGame 3: RPG w/ better storyGame 4: RPG w/ better gameplayGame 5: My First MMORPGGame 6: My Second MMORPG, CLANS!Game 7: My Third MMORPH, Many features!!!Game 8: My Fourth MMORPG, I WILL CHARGE FOR THIS ONE!!!

I would change Game 1 to "simple RPG". When I hear RPG, I think 40+ hour Final Fantasy game. My first and current game (that I've been working on for almost 15 months now) is a long, fully-featured RPG. And you know what? Those take a lot of time to develop, especially when its your first shot at things. I would advice people to develop an RPG that maybe has one town, one dungeon, and one short and sweet ending. That shouldn't take too long to build, as long as you don't try to make the graphics/etc overly complex.

Anyway I'm done rambling. Its bed time [smile]

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 For example, Game 1: RPGGame 2: RPG w/ better graphicsGame 3: RPG w/ better storyGame 4: RPG w/ better gameplayGame 5: My First MMORPGGame 6: My Second MMORPG, CLANS!Game 7: My Third MMORPH, Many features!!!Game 8: My Fourth MMORPG, I WILL CHARGE FOR THIS ONE!!!

That is the secret to successful game dev right there. Good call! :D

Personally, I think it could even be started lower. My first release for testing will be a town. No quests, no plot, no NPC banter. Just a character, buildings, a place to shop, a place to sleep, and a place to hunt monsters (sewer, forest, the grassy patch just outside the city limits). Done. At least then, players are able to kill, loot, upgrade, repeat. Cliche' as it is, it gives them something playable. Then the developer can slowly add NPCs, NPC text, a few simple quests, a larger area outside of town, etc.

Starting low like that has a few benefits. It allows players into the game early to start finding bugs, which minimizes the impact later. It allows players to make suggestions early on, which allows for more efficient game design. And it allows people to see that youve made progress and have actually completed something, which will bring in extra help. ;)

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 Poor managment is what makes what I would say 80% of these projects end.

People seem to neglect how important management is. When I went to college for 'digital media arts' I had three management related projects rolled into my program. One for project management, one for business communication and a final one for general business concepts and problem solving. Though a lot of my classmates slept through these classes (big words cause art students to zone out) I really appreciated what I learned there. The fact is, getting the neccesary talent for a game is only half the battle. You need to manage that talent to succeed. Achievable time-based goals need to be set, team members need constant direction and ideas need to be scaled, revised and (most importantly) finalized. Otherwise your team is just sitting around, never getting anything substantial done.

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Original post by Omegavolt
Quote:
 For example, Game 1: RPGGame 2: RPG w/ better graphicsGame 3: RPG w/ better storyGame 4: RPG w/ better gameplayGame 5: My First MMORPGGame 6: My Second MMORPG, CLANS!Game 7: My Third MMORPH, Many features!!!Game 8: My Fourth MMORPG, I WILL CHARGE FOR THIS ONE!!!

That is the secret to successful game dev right there. Good call! :D

Personally, I think it could even be started lower. My first release for testing will be a town. No quests, no plot, no NPC banter. Just a character, buildings, a place to shop, a place to sleep, and a place to hunt monsters (sewer, forest, the grassy patch just outside the city limits). Done. At least then, players are able to kill, loot, upgrade, repeat. Cliche' as it is, it gives them something playable. Then the developer can slowly add NPCs, NPC text, a few simple quests, a larger area outside of town, etc.

Starting low like that has a few benefits. It allows players into the game early to start finding bugs, which minimizes the impact later. It allows players to make suggestions early on, which allows for more efficient game design. And it allows people to see that youve made progress and have actually completed something, which will bring in extra help. ;)

This post reminded me about Diablo. It is basically this idea but on many game levels. One town where you return to sell and recover, and back again.

Many companies have started that way, focusing on a single line. But taking again Blizzard as an example, you have an excellent example of progression. Warcraft, Warcraft2, Diablo, Starcraft, Diablo2, Warcraft3. All a line of tile based games improved in each release. Everyone should start this way.

But the most important thing here is FINISH SOMETHING PLEASE!!! Once I thought that programming my game engine was difficult. Now, after years of programming my MMOG, If you ask me... I would use an already made engine instead of trying to make one myself :P

Luck!
Guimo

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Hell I've been making small games for over 10 years and find it hard to complete a project. Suffice to say I'm not going to be aiming for the MMORPG any time in the next 50 years. Ignorance is bliss.

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I think it has to do with the fact the people want to make games that they would want to play. And since so many people are playing MMO these days its natural that there is so many people out there wanting to make their own MMO.

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One thing to remember on this forum is not everyone who posts the newest MMO idea is trying to make one (alot are, but not all)

Some of us, have no clue on programming, nor any plan to make an MMO.

However, we do have ideas, and post them. For us its like a hobby of creativity.

I have alot of ideas floating around. Will I make one...no. But I like posting the idea...besides someone may say...HEY thats a cool idea, I like it.

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Quote:
Original post by Omegavolt
Quote:
 For example, Game 1: RPGGame 2: RPG w/ better graphicsGame 3: RPG w/ better storyGame 4: RPG w/ better gameplayGame 5: My First MMORPGGame 6: My Second MMORPG, CLANS!Game 7: My Third MMORPH, Many features!!!Game 8: My Fourth MMORPG, I WILL CHARGE FOR THIS ONE!!!

That is the secret to successful game dev right there. Good call! :D

Personally, I think it could even be started lower. My first release for testing will be a town. No quests, no plot, no NPC banter. Just a character, buildings, a place to shop, a place to sleep, and a place to hunt monsters (sewer, forest, the grassy patch just outside the city limits). Done. At least then, players are able to kill, loot, upgrade, repeat. Cliche' as it is, it gives them something playable. Then the developer can slowly add NPCs, NPC text, a few simple quests, a larger area outside of town, etc.

Starting low like that has a few benefits. It allows players into the game early to start finding bugs, which minimizes the impact later. It allows players to make suggestions early on, which allows for more efficient game design. And it allows people to see that youve made progress and have actually completed something, which will bring in extra help. ;)

That is a good explanation, Omega. That design is so effective. But since it's so simple, many people, such as noobs, think that "simple" design is stupid and underrated. Too bad for them they're wrong. I think that if anyone's going suceed in any type of MMO, they need to start making game, gain experience, and gain some common sense that making large games like that will lead ignorant teams, or person, to oblivion. Lol. I always wanted to say that.

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The simple start is what I have in mind for my MMORPG. I plan on starting with a town in a text based RPG and NOTHING more. You will be able to move around and look at things.

When that works I'll add in shops and things like dart boards or training facilities. With these implemented I have combat implemented. With combat, the hunting grounds are added.

Next is mining facilities where players can go mine stuff, followed by allowing players to purchase mining equipment and mine and build their own buildings.

And so on, I prefer the itterative approach as opposed to trying to do everything at the start.

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Quote:
 Original post by robert4818One thing to remember on this forum is not everyone who posts the newest MMO idea is trying to make one (alot are, but not all)Some of us, have no clue on programming, nor any plan to make an MMO.However, we do have ideas, and post them. For us its like a hobby of creativity. I have alot of ideas floating around. Will I make one...no. But I like posting the idea...besides someone may say...HEY thats a cool idea, I like it.

true, i enjoy brainstorming for ideas. I enjoy designing games even if they wont ever get made.

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Thank you for all the constructive replies...I will now take the time to reply to all of you.

ace_lovegrove: I can definatly understand your point of view.
This is a large, complex, and limitless industry...and leads to multiple concepts.

Sol462: Finally, I thought I was the only one who noticed this trend.

acraig: That is very fortunate of you, but still can you imagine the fact that there are 100's of these projects out there...and only about 1 out of every 100 make any progress at all...and only 1 out of every 100 of those make it to complete!

Thats way less then a 1% chance of making it!

Trapper Zoid: Yes that is most definatly the reason why they try to make these games.
But what they don't realise is that if they cant make something simple, there is 0 chance of making it full time.

Roots: Oh, hmm well when I here RPG I think Walk around, beat up bad guys, and talk to strangers....as well as a normal young boy has a big tragety and now he is this mystic warrior.

Omegavolt: Right, well as I said before people have no patients to start with those simple things like that.
So the thing is, I would start out with the most basic of basic rpg.

Radiostorm: I am glad to see you agree with me.
And where did you go to school?

Guimo: Hmm, thats another thing.
Most people want an origanal game engine, which is very sickening being as that even the most simplest of 2D game engines are hard to make...let alone a next gen 3D game engine, with physics, and ai!

evolutional: I got a good laugh out of that one...
10 years is alot of experience, what games have you made!

TechnoGoth: As I said to TrapperZoid, that is 100% the reason why they want to do that.

robert4818: Right, but if you look at the help wanted forum, all you see is "H3lp m3 with me MMORPG!!!!111one"

Zido: Erm, well I guess that post isnt directed to me, so I wont reply.

Drethon: Where is this game, I might be interested in playing it.

Riviera Kid: That post wasn't directed towards me, so I will not reply

OK, thank you all for the great post.
Keep it up, I would love to see this post evolve more on.

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 Radiostorm: I am glad to see you agree with me. And where did you go to school?

Seneca College in Ontario, Canada. I took their two year digital media arts program. < http://www.senecac.on.ca/fulltime/DMA.html >

There was a lot of emphasis on project management in addition to practical application of software. A good portion of my project marks were based on my process, planning, rough work, storyboards and idea maps. I was even thrust into the role of a project manager over several classmates in a few instances. My professors were really intent on ingraining the importance of project management into our jaded art student minds.

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Actually, the single biggest hurdle to making a small 3D MMO is the amount of art needed. Characters, weapons, items, monsters, environments, interface, effects, ... it just goes on. While some good programmers happily work for free in their spare time, most artists don't seem to want to do that. I think they're smarter than us ;-)

Now, here's where money comes in: if you have money, you can pay artists. And that's where management comes in, because you can't have other people giving you money unless you have your act together. Pretty soon, the whole thing snowballs and it grows too big for an indie.

There are some exceptions. PlaneShift is one; RuneScape is another (it's indie, but it's been around for a while). There are some MMOs that use 2D, or are set in space, or otherwise chooses to not have the challenges of a typical 3D MMO, too.

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The game I'm working on is still in the development phase, I'm spending more time working on Conflict Omega (www.conflictomega.com) at the moment.

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Hmm, seems we have 3 more comments.
Ok well I will try my best to reply.

RadioStorm: Thanks, sorry for the random gest.
I was just curious is all.
I am interested in not only checking ones experience, but where there background is as well.

Its more of a "Does this school teach well, or not" kind of thing.
I always put myself as if I was a corporation (alas I am not) and If I was hiring I would look more into your school to find out the success ratio, any famous developers from the school, and the average game style that is spawned from that company to compare if it's compatable with mine.

Research is another great aspect I noticed many game developers (some professional corperations as well) don't put into view.

hplus0603: I must agree with the art part, but I can not find A single programmer at all.
May it be from the fact that I myself do not know how to program well? (I can basicly read it, but not code)

Drethon: I will check that game out, see what it's all about.
If possible I would like to maybe even play it when/if it's released (if as in If it is currently released, not as in if it ever will be)

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I am very new here and I would like to share something I see as a flaw (please correct me if I am wrong)

I do not see anything truely focused on the testing side of developing these MMO games... I seriously think that folks in general do not understand the scope of their own game enough. If this is the case, how can we expect them to be tested effectively? The trend I see currently, Thanks to UO and EQ1, is that pushing broken systems is ok because the users will figure out the bugs... am I the only one here that sees this?

Sorry I cannot go into too much depth but I am working ATM :D


text:
Limit theorems for Markov processes indexed by continuous time Galton-Watson trees - Archive ouverte HAL Access content directly
Journal Articles Annals of Applied Probability Year : 2011

Limit theorems for Markov processes indexed by continuous time Galton-Watson trees

(1) , (2) , (3) , (1, 3)
1
2
3
Vincent Bansaye
• Function : Author
• PersonId : 864596
Jean-François Delmas
• Function : Author
• PersonId : 933972
Laurence Marsalle
• Function : Correspondent author
• PersonId : 864597

Connectez-vous pour contacter l'auteur
Viet Chi Tran

Connectez-vous pour contacter l'auteur

Abstract

We study the evolution of a particle system whose genealogy is given by a supercritical continuous time Galton-Watson tree. The particles move independently according to a Markov process and when a branching event occurs, the offspring locations depend on the position of the mother and the number of offspring. We prove a law of large numbers for the empirical measure of individuals alive at time $t$. This relies on a probabilistic interpretation of its intensity by mean of an auxiliary process. This latter has the same generator as the Markov process along the branches plus additional branching events, associated with jumps of accelerated rate and biased distribution. This comes from the fact that choosing an individual uniformly at time $t$ favors lineages with more branching events and larger offspring number. The central limit theorem is considered on a special case. Several examples are developed, including applications to splitting diffusions, cellular aging, branching Lévy processes and ancestral lineages.

Dates and versions

hal-00431118 , version 1 (10-11-2009)
hal-00431118 , version 2 (02-08-2010)

Identifiers

• HAL Id : hal-00431118 , version 2
• ARXIV :
• DOI :

Cite

Vincent Bansaye, Jean-François Delmas, Laurence Marsalle, Viet Chi Tran. Limit theorems for Markov processes indexed by continuous time Galton-Watson trees. Annals of Applied Probability, 2011, 21 (6), pp.2263-2314. ⟨10.1214/10-AAP757⟩. ⟨hal-00431118v2⟩

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# How to Convert RPM to Feet per Minute

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Print

The spinning of a disk on a shaft often translates to linear motion. The most obvious example is an automobile wheel, but forward motion can also be important when designing gear and belt systems. The translation from rotation to linear speed is straightforward; all you need to know is the radius (or diameter) of the spinning disk. If you want the linear speed in feet per minute, it's important to remember you need to measure the radius in feet.

#### TL;DR (Too Long; Didn't Read)

For a disk spinning at n rpm, the forward speed of the attached shaft is n × 2πr if the radius of the disk is r.

## The Basic Calculation

Designate a point P on the circumference of a spinning disk. P makes contact with the surface once with each spin, and with each spin, it travels a distance equal to the circumference of the circle. If the frictional force is sufficient, the shaft attached to the disk moves forward that same distance with each rotation. A disk with radius r has a circumference of 2πr, so each rotation moves the shaft forward that distance. If the disk spins n times per minute, the shaft moves a distance n × 2πr each minute, which is its forward speed (s).

s = n × 2πr

It's more common to measure the diameter (d) of a disk, such as a car wheel, than the radius. Since r = d ÷ 2, the forward speed of the car becomes nπd, where n is the rotational speed of the tire.

s = n × πd

## Example

A car with 27-inch tires is traveling 60 miles per hour. How fast are its wheels spinning?

Convert the car's speed from miles per hour to feet per minute: 60 mph = 1 mile per minute, which in turn is 5,280 ft/min. The car's tire has a diameter of 1.125 feet. If s = n × πd, divide both sides of the equation by πd:

n = \frac{s}{πd} \\ \,\\ = \frac{5280 \text{ ft/min}}{3.14 × 1.125 \text{ ft}} \\ \,\\ = 1,495 \text{ rpm}

## Friction Is a Factor

When a disk in contact with a surface rotates, the shaft around which the disk is spinning moves forward only if the force of friction between the disk and surface is large enough to prevent slipping. The frictional force depends on the coefficient of friction between the two surfaces in contact and on the downward force exerted by the weight of the disk and the weight applied to the shaft. These create a perpendicular downward force at the point of contact called the normal force, and this force becomes less when the surface is inclined. A car's tires can start slipping when the car climbs a hill, and they can slip on ice, because the coefficient of friction of ice is less than that of asphalt.

Slippage affects forward motion. When translating rotational speed into linear speed, you can compensate for slippage by multiplying by an appropriate factor derived from the coefficient of friction and the incline angle.

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# zbMATH — the first resource for mathematics

A new fast algorithm for the unified forward and inverse MDCT/MDST computation. (English) Zbl 1007.94521
Summary: The modified discrete cosine transform (MDCT) and modified discrete sine transform (MDST) are employed in subband/transform coding schemes as the analysis/synthesis filter banks based on the concept of time domain aliasing cancellation. Princen, Bradley and Johnson defined two types of the MDCT, specifically, for an evenly stacked and oddly stacked analysis/synthesis system. The MDCT is the basic processing component in the international audio coding standards and commercial products for high-quality audio compression. Almost all existing audio coding systems have used the complex-valued or real-valued FFT algorithms, and the DCT/DST of type IV for the fast MDCT computation. A new fast and efficient algorithm for a unified forward and inverse MDCT/MDST computation in the oddly stacked system is proposed. It is based on the DCT/DST of types II and III, and real arithmetic is used only. The corresponding generalized signal flow graph is regular, structurally simple and enables MDCT/MDST and their inverses to be computed in general for any $$N$$ divisible by 4 ($$N$$ being the length of a data sequence). Consequently, the new fast algorithm can be adopted for the MDCT computation in the current audio coding standards such as the MPEG family, and in commercial products (proprietary audio coding algorithms). Besides, the new fast algorithm has some interesting properties, and it provides an efficient implementation of the forward and inverse MDCT computation for layer III in MPEG audio coding, where the length of data blocks $$N\neq 2^{n}$$. Especially, for the AC-3 algorithm, it is shown how both the proposed new MDCT/MDST algorithm and existing fast algorithms/computational architectures for the discrete sinusoidal transforms computation of real data sequences such as the DCT-IV/DST-IV, generalized discrete Fourier transform of type IV and generalized discrete Hartley transform of type IV can be used for the fast alternate or simultaneous (on-line) MDCT/MDST computation by simple pre- and post-processing of data sequences.

##### MSC:
 94A12 Signal theory (characterization, reconstruction, filtering, etc.) 65T50 Numerical methods for discrete and fast Fourier transforms
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class torch.nn.AdaptiveMaxPool2d(output_size, return_indices=False)[source]

Applies a 2D adaptive max pooling over an input signal composed of several input planes.

The output is of size H x W, for any input size. The number of output features is equal to the number of input planes.

Parameters
• output_size – the target output size of the image of the form H x W. Can be a tuple (H, W) or a single H for a square image H x H. H and W can be either a int, or None which means the size will be the same as that of the input.

• return_indices – if True, will return the indices along with the outputs. Useful to pass to nn.MaxUnpool2d. Default: False

Examples

>>> # target output size of 5x7