# Tagged Questions

Questions on the manipulation of matrices in Mathematica.

6answers
4k views

### Elegant operations on matrix rows and columns

Question The Mathematica tutorial has a section 'Basic Matrix Operations', describing operations like transpose, inverse and determinant. These operations all work on entire matrices. I am missing a ...
4answers
727 views

### Why does MatrixForm affect calculations?

This is a really newbie question, but it has me confused. Why does this code work without // MatrixForm and doesn't work with ...
2answers
939 views

### Cycles of length N in a graph

If I have an undirected graph represented with an adjacency matrix, how can I find all the subgraphs which are a cycle of length N? I don't really know the math nor the programming language well, so ...
3answers
1k views

### How to symbolically do matrix “Block Inversion”?

Consider a block (partitioned) matrix matrix = ArrayFlatten[{{a, b}, {c, d}}] where, a, ...
6answers
2k views

### Does Mathematica have advanced indexing?

I have two $M \times K$ arrays $L, T$ where I would like to set all the elements in $L$ to zero whenever the corresponding element of $T$ is greater than 15. The ...
2answers
590 views

### Tiling a square

I wondered if there was a way to automate the process of finding a way to tile a tile into a square. The idea is to represent the tile with a matrix of 0s for blank space and 1s for filled spaces ...
6answers
1k views

### How to visualize/edit a big matrix as a table?

Is it possible to visualize/edit a big matrix as a table ? I often end up exporting/copying big tables to Excel for seeing them, but I would prefer to stay in Mathematica and have a similar view as in ...
5answers
953 views

### What is the most efficient way to add rows and columns to a matrix?

Say I have a matrix m and a vector v. ...
2answers
971 views

### How to enter matrices in block matrix format?

Example: I have a matrix $R = \left( \begin{array}{cc} A & \mathbf{t} \\ 0 & 1 \end{array} \right)$ where $A$ is 3-by-3 and $\mathbf{t}$ is 3 by 1. Or in Mathematica ...
4answers
3k views

### Creating a table/Matrix during a For loop

I have a For loop (with i as a counter), which calculates different values (y1, ...
1answer
344 views

### Nesting Parallel processes

I just attempted to run code that had nested ParallelMap[] functions. It generates the error message: ParallelMap::subpar: Parallel computations cannot be nested; proceeding with sequential ...
2answers
552 views

### Non-commutative symbolic linear algebra

I am fairly new to Mathematica but I thought I would be a helpful tool to carry out a few simple linear algebra calculations. It seems like an easy task but I cannot figure out how to do it. For ...
4answers
499 views

### What is the fastest way to locate an image inside a larger image?

let b = let c = How to do: find[c,b] that returns the bounding box of c in b? ...
3answers
514 views

### Correcting a correlation matrix to be positive semidefinite

Does Mathematica have a way to "fix" a correlation matrix that is not positive semi-definite? I looked through the documentation and search the internet but could not find anything.
2answers
886 views

### How to get Matlab data imported with the same dimensions?

I have some Matlab image data with the following dimensions (output is from Matlab): >> size(im) ans = 86 86 3 45 The data imports just fine ...
1answer
255 views

### How to extract and replace submatrix of a doubly-periodic matrix?

How can I effectively extract and replace a rectangular subpart of a toroidal matrix, i.e. one where boundaries are connected at opposite ends? Since the submatrix can overhang the edges, a simple ...
2answers
451 views

### How to use a 3×3 covariance matrix to plot an error ellipsoid?

I have a 3×3 error covariance in Mathematica, but I don't know how to use it for plotting the error ellipsoid. It would be great if you can show me how I can do that for the below covariance matrix: ...
1answer
434 views

### Mathematica won't give eigenvectors but Wolfram Alpha will? What am I doing wrong?

If I ask Mathematica to find the eigenvectors and eigenvalues of the matrix: ...
2answers
371 views

### Entering block matrices for an arbitrary matrix size

Background: How to enter matrices in block matrix format? and the following: I want to create $$f(A,t) = \left [ \begin{matrix} A & t \\ 0 & 1 \end{matrix} \right ]$$ where $A$ ...
3answers
322 views

### How to manipulate gauge theory in Mathematica?

I want to know if there is a way of typing into Mathematica an expression like the following, \epsilon^{\mu \nu \lambda} f^{abc} A^a_\mu A^b_\nu A^c_\lambda + g\epsilon^{\mu \nu \lambda} A^a_\mu ...
3answers
191 views

### How to sum matrix elements based on finding the first (and second) non-zero elements of each row?

I have a matrix: I would like to sum all the first non-zero elements of each row so that I get a value of $$25.5317 + 8.85471 + 6.90018 + 32.9436 + ...$$ and so on and simply ignore zero rows. ...
2answers
325 views

### Why don't * and ^ work as I expected on matrices?

For example, this input... {{1, 2}, {3, 4}}*{{1, 2}, {3, 4}} produces this output... {{1, 4}, {9, 16}} and this input... ...
4answers
305 views

### How do you decompose a polynomial matrix into its matrix coefficients?

Let's say I have a matrix, $\mathbf{M}$, that is polynomially dependent on a single variable, such as M = {{15 + a^2, a + 5 a^2}, {a - 5 a^2, 2}} and I want to ...
2answers
339 views

### How to form a block-diagonal Matrix from a list of matrices? [duplicate]

like this: I know join[...] works, but it is a bit troublesome for multiple matrices.I tried DiagonalMatrix[...], but DiagonalMatrix can only form matrix from a list of elements.
4answers
221 views

### How to transform this matrix & swap its columns in a simple way?

I would like to transform matrix $\mathbf A = \begin{pmatrix} a&b&i&j\\ c&d&k&l \\ e&f&m&n \\ g&h&o&p \end{pmatrix}$ into matrix \$\mathbf B = ...
4answers
430 views

### How do I generate the upper triangular indices from a list?

I have some list {1,2,3}. How do I generate nested pairs such that I get {{1,2},{1,3},{2,3}}? That is I'd like a way to ...
5answers
881 views

### Best way to create symmetric matrices

From time to time I need to generate symmetric matrices with relatively expensive cost of element evaluation. Most frequently these are Gram matrices where elements are $L_2$ dot products. Here are ...
2answers
206 views

### All possible solutions to the Matrix Equation (free variables appearing)

I am attempting to solve a system of linear equations using LinearSolve[] . In my case, the number of unknowns are more than constraints. I learnt that LinearSolve ...
4answers
266 views

### Prepend 0 to sublists

My question is similar to this one, but my goal is to prepend a single 0 the each sublist, not incrementally many 0's. The file I'm working is a CSV containing around 50K sublists of length 35. I've ...
2answers
472 views

### Using the Krylov method for Solve: Speeding up a SparseArray calculation

I'm trying to implement this Total Variation Regularized Numerical Differentiation (TVDiff) code in MMA (which I found through this SO answer): essentially I want to differentiate noisy data. The full ...
3answers
436 views

### Constructing a symbolic Hermitian matrix

I need to construct a symbolic Hermitian matrix like m = { { n, a, b, b}, {Conjugate[a], n, b, b}, ... } but I am not able to set ...
4answers
281 views

### Inputting a big structured matrix in Mathematica

Hi this is my first post and this is a problem that has bothered me a lot. Suppose we have the $2012\times2012$ square matrix: ...
2answers
191 views

### Correct way to generate large data sets (i.e.forward yield curve )

I would like to generate a set of forward yield curve matrix of size 1000 x 100. First I defined my SparseArray of 1000 x100: ...
2answers
131 views

### How to use “Drop” function to drop matrix' rows and columns in an arbitrary way?

The built-in function "Drop" can delete a Matrix's row and column. Typical syntax for "Drop" is as follows: Drop[list,seq1,seq2...] But what if I want to drop a ...
1answer
385 views

### stationary distribution of a transition matrix

How can I solve the stationary distribution of a finite Markov Chain? In other words, how can I estimate the eigenvectors of a transition matrix?
3answers
555 views

### Passing a matrix as a function argument

I am trying to do the following: ...
1answer
222 views

### Efficiently Constructing Rank One Approximations for a Matrix using SVD

Suppose I have a $m\times n$ matrix $A$ (real for simplicity). Then SingularValueDecomposition[A] yields 3 matrices $U$, $\Sigma$ and $V$ such that \$A = U\Sigma ...
2answers
161 views

### Sort matrix by columns and rows without changing them

I would like to sort a matrix in descending order first by the total of each column, then by the total of each row, but without changing their content. For example, if I had: ...
3answers
278 views

### How do we solve Eight Queens variation using primes?

Using a $p_n$x $p_n$ matrix, how can we solve the Eight queens puzzle to find a prime in every row and column? ...
4answers
907 views

### How to convert equation to vector (matrix) form?

How can I convert expression a1*u1+a2*u2+a3*u3 to the vector form of dot product A.U, where ...
2answers
231 views

### Dynamic matrix multiplication

I have the following problem: I want to multiply two matrices and sum them to another matrix C. A.B+ 2B Easy! The matrix A varies as a function of three inputs a,b and c. The second matrix, B, is a ...
2answers
264 views

### Loop and do operations on Matrix, then graph the results

I'm trying to do some operations to a matrix in a loop, and then I want to graph the results. The results are pair of numbers. Can I store the results of each iteration on "something" and the use ...
2answers
239 views

### A dot appearing after a zero, and making the entries of a matrix into fractions

For more info about the difference between 0. and 0 I am a self-taught Mathematica user and I have some elementary questions-- perhaps too elementary for this site, but here they are. If ...
3answers
269 views

### Is there a way to do conditional matrix loop using 'continue'

I have the following: ...
1answer
126 views

### Numerical comparisons of matrices

I have a matrix which should be equal to a null matrix. However due to the numerical precision, a brutal equality test with a matrix initialized with zeros does not work. How should I perform the ...
2answers
533 views

### Matrix multiplication in Block Form symbolic calculation by Mathematica

I have a problem which requires taking product of two $10\times10$ matrices. I would like to do it by considering both matrices as $5\times5$ matrices such that each entry of both matrices is actually ...
2answers
177 views

### Symbolically associate vectors and their norms

I am wondering how to handle the following situation: I do have vectors of known dimension that I would like to handle symbolically. I suppose I can do something like ...
1answer
133 views

### How to do nor on matrices?

Supose I have matrices a b and c like a = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}; b = {7, 8, 9}; c = {{1},{4},{7}}; I want to get ...
2answers
136 views

### Correct way to compare arrays and do conditional evaluations

I would like to compare two arrays a=: and b= and get: using: (b/.(b_?Positive->a+b))//MatrixForm but this doesn't seem to work? Can ...
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