# Tagged Questions

Questions on the use of Mathematica to construct models for approximating empirical data. (FindFit[], Fit[], LinearModelFit[], NonlinearModelFit[], etc.)

4answers
818 views

### How to visualize 3D fit

I have a data set of x,y,z values and I fit a function of x,y to the data. This works, but I can't come up with a nice way to ...
4answers
2k views

### Simultaneously fitting multiple datasets

What is the proposed approach if one wants to simultaneously fit multiple functions to multiple datasets with shared parameters? As an example consider the following case: We have to measurements of ...
3answers
836 views

### Data fitting with Image processing feature detection

I have some 2D data that once plotted looks like the following ...
2answers
610 views

### Finding the area, algebraic curve and jaggedness of an arbitrary shape

I start with a photograph of a shape (physically made by the flow of a liquid into another), of which I can extract the border, manually or using Mathematica's feature detect feature : Using the ...
1answer
504 views

### Compact Rational Function Fitting

I have some data from a study that I am trying to fit with a rational function of arbitrary form: $y(x) = \frac{\sum_{i=n}^m A_ix^{i/q}}{\sum_{j=o}^p B_jx^{j/r}}$ where $i$, $j$, $k$, $l$, $m$, $n$, ...
2answers
569 views

### FindFit returns Infinity::indet error when data contains {0,0}

Let's consider the following data: data = Table[{q, 2*q^2}, {q, 0, 2}]; and then, do a very simple fitting to this data: ...
3answers
763 views

### Mathematica envelope for the bottom of a plot, a generic function

I have the following set-up: xaxis = Table[x, {x, 0, 10, 0.01}]; yaxis = Table [Sin[x] + Abs[RandomReal[{-1, 1}]], {x, 0, 10, 0.01}]; ListLinePlot[Transpose[{ xaxis, yaxis}]] My ...
5answers
2k views

### Estimate error on slope of linear regression given data with associated uncertainty

Given a set of data, is it possible to create a linear regression which has a slope error that takes into account the uncertainty of the data? This is for a high school class, and so the normal ...
3answers
573 views

### Finding a fit to a multi-dimensioned function

I have a model function $f:\mathbb{R}^2\rightarrow\mathbb{R}^2$, and a bunch of data points for which I'd like Mathematica to fit for me. Unfortunately FindFit ...
4answers
2k views

### Problem with NonlinearModelFit

I'm having trouble with a non-linear fit: fit = NonlinearModelFit[data, y0 + A Sin[\[Pi] (x - xc)/w], {y0, xc, A, w}, x] where ...
4answers
2k views

### Using FindFit to fit $a\,b^t$: how to avoid introducing complex numbers?

I'd like to find a model $f(t)=a\,b^t$ which matches the following data ...
2answers
403 views

### Trying to fit an unknown extreme distribution

First up, I'm quite new to Mathematica so any hints on better code would be greatly appreciated. I have some histogram frequency data from an unknown distribution that I'm trying to fit. Here's the ...
4answers
603 views

### Mathematica Implementations of the Random Forest algorithm

Is anyone aware of Mathematica use/implementation of Random Forest algorithm?
3answers
677 views

### How to use FindFit to fit an implicit function?

Now I am trying to fit some data with a implicit model function. Firstly, I tried a toy example. Toy example with input and output ...
2answers
256 views

### Unexpected differences with various uses of NormFunction

I would expect all of the following to give the same answer (2.12467) but only half of them give this answer. The others seem to be using the default ...
3answers
803 views

### Fitting fractional complex data with NonlinearModelfit

I've difficulites with the NonlinearModelFit function. In principle Mathematica should be able to deal with complex data. E.g. if I define the following table ...
1answer
724 views

### Fitting a spline to data with FindFit?

I am trying to find a function that fits my almost linear data. A high order polynomial model has too much residual. So I was hoping to use Mathematica to fit splines to the curve. This is what I ...
3answers
437 views

### Ηow to create an interpolated CDF from its samples?

I want to use a distribution I have only aggregate statistics on, namely its CDF sampled at certain points. I would like to keep it "nonparametric" (remain noncommittal on the parametric form), but I ...
2answers
302 views

### Is it possible to use the LevenbergMarquardt algorithm for fitting a black-box residual function?

I have a black-box multiargument multiparametric function of the type SRD[dataPoint_List,params_List] which accepts experimental data along with the parameters of ...
4answers
816 views

### Can one force a linear regression fit to go through the origin?

As the question says, can one force a fit through the origin $(0,0)$ as one can when fitting a trendline to your data in MS Excel? If so, how do you do that?
6answers
1k views

### How to determine the center and radius of a circle given three points in 3D?

I was wondering if anyone could give me a hand with this problem I have. I have six points on a plane, and I am trying to determine if they form a circle or not. I know that any three points in 2D ...
2answers
484 views

### FindFit returns worse result when putting constraints on parameters

I want to fit some data to a model of exponential decay using the FindFit function: ...
1answer
136 views

### Obtaining standardised regression coeffiecients

Regression coefficients are the constant that indicate the rate of change in one variable as a function of change in another. Standardised regression coefficients are the same, but refer to a change ...
1answer
112 views

### Smoothing/Averaging 2D Vector Fields

I have a list of 2D vectors defined by {{x,y},{u,v}} and would like to smooth or average the vectors. For example here are 2 vector fields, the second has noise ...
1answer
187 views

### Fix end point in smooth kernel distribution density

I am using some extreme value fitting method which results in a parametric distribution for values exceeding some threshold, all values $\geq 0$. For smaller values I'd like to use a smooth kernel ...
2answers
599 views

### NonlinearModelFit Problem

I have some problems with the NonlinearModelFit: NonlinearModelFit[data, A (1 + Cos[a x]) + B (1 + Cos[b x]) + c , {A, B, a, b, c}, x] The model should fit my ...
3answers
529 views

### Finding the linear regression of data and plotting it

This is for a physics report that I have to hand in. I have a list of two-dimensional data points that approximately form a linear line. I want to: calculate the best linear fit. put both data ...
1answer
140 views

### LinearModelFit with millions of rows

I'd like to do a simple regression with millions of rows of (x,y) data. It seems to be too long for Mathematica. Is there a way to speed it up? It shouldn't be that hard to do, I am not sure what ...
2answers
232 views

### How to find Matano plane

I have discrete collection of data points (10 to 10^4). I want to describe them by a continuous function and find a x value z, ...
2answers
319 views

### In finding a logarithmic fit for some data (of the form a*Log[b*x]), WolframAlpha succeeds where Mathematica 7.0 fails, why?

I would like to fit a function of the form: $a \log(b x)$ to a set of data: ...
1answer
134 views

### Specify a constraint on an interval under FindMinimum

I have an interpolated function that looks like this: $\hskip1.2in$ and, based on extreme and critical points, I want to use a polynomial to approximate the function. The points in question are: ...
0answers
61 views

### Using perpendicular offsets in FindFit

I want to use perpendicular offsets in the built-in FindFit function. Are there any possible ways or do I have to code everything by myself?
0answers
191 views

### Mathematica vs Sigmaplot (Non LinearModelFit)

I asked a question in a previous post that was closed because "The title of the question is not correct and the issue here is too trivial to help anyone later". NonLinearModelFit It's possible ...
0answers
224 views

### NonlinearModelFit weights

I would like to know how to perform a nonlinear regression on a table with measurement errors. The table consists of two columns, and both have errors. I've been watching some tutorial and it is very ...
3answers
382 views

### Output of NonlinearModelFit differs from the correct result

I'm having a bad time dealing with the NonlinearModelFit in Mathematica 8, since the result given is a bit imprecise. An example is given on potential regression, ...
1answer
462 views

### NonlinearModelFit::cvmit: Failed to converge to the requested accuracy or precision within 100 iterations

I have got a problem in my program with NonlinearModelFit: ...
1answer
127 views

### Multinomial logistic regression

Has anyone done multinomial logistic regression in Mathematica? The binomial case is essentially done on the LogitModelFit documentation page and works fine. I am ...
2answers
159 views

### What can I do to eliminate the error FindFit::nrjnum:?

I am testing the "Power Law with finite-time singularity" hypothesis for world population growth for a project. The data I'm using (same behaviour should also be exhibited by the stock market, thats ...
1answer
231 views

### Time approximation of decrypting RSA algorithm

I've written a function that encrypts a text using the RSA algorithm. It then decrypts it using prime factorization, and takes the time it took to decrypt it and puts it in a vector together with the ...
0answers
452 views

### Analytical model fitting

I have a special type of model fitting problem that I am trying to solve in Mathematica. Any insight how to attack it using available tools of Mathematica will be great to hear. We have a variable  ...
4answers
159 views

### Remove linear trend from data

I have a large data set with 150k lines and two data columns. I noticed that there is a linear trend, which I want to remove. So, I do the following: first fit with a linear model ...
1answer
143 views

### Getting slightly different results in fitting a logit model in R and Mathematica

I'm fitting some data to a Logit model in both Mathematica and R and I'm getting slightly different results. R code: ...
5answers
411 views

### How to plot Fit functions?

If I do something like this f[x_]:=x^2 Plot[f[x],{x,1,10}] Mathematica plots the function $f(x)=x^2$, as expected. However, ...
2answers
116 views

### Linear regression in a chosen range of points

Hi I'm absolutely newbie in Mathematica and have following problem: My list looks like {{50, 0.75}, {51, 0.76}, ..., and I want to choose a range out of my ...
1answer
85 views

### Does LinearModelFit perform an ordinary linear regression (least squares)?

Does LinearModelFit give an ordinary linear regression? I see lots of options, but nothing like "least squares" or OLR.
1answer
387 views

### How do I find the best parameter to fit my data if the model is a interpolating function?

Hi I have a question regarding to find the best parameters for my model to fit my data. I have 3 ordinary equation, and I now just picked some parameters (...
1answer
118 views

### NonlinearModelFit returning nonsense for very simple data

In fitting the following data, if I first log transform the y-values and use LinearModelFit I get a set of parameters that fits the data: ...
1answer
294 views

### Why FindFit could not exactly fulfill condition?

I tried to fit some data with boundary conditions, but FindFit just could not work. Does anyone know the reason? Details: The function to be fitted is ...
1answer
123 views

### Error message from evaluating NonlinearModelFit

I am trying to fit data to a Morse potential using NonlinearModelFit as follows: ...
0answers
154 views

### Mathematica Complains about Non Symmetric Covariance matrix, when it's not the case

I was doing some fitting with Mathematica7 using NonlinearModelFit. It's quite long the program to do the fit and that's why I am not displaying here ... It goes ok, and I can get the fit parameters ...
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