Questions on the manipulation of matrices in Mathematica.

learn more… | top users | synonyms (1)

3
votes
1answer
79 views

Plotting eigenvalues smoothly

I am trying to plot how the eigenvalues of a matrix change by changing a given a parameter t. Of course the ordering of the eigenvalues does not matter mathematically but it does when I want to make ...
1
vote
1answer
64 views

Creating a transformation matrix with respect to given bases? [closed]

Let's say I have a linear transformation $T:V\to W$, along with some bases $\{v_1,v_2\}$ and $\{w_1,w_2,w_3\}$ of each respectively. Let's say all the information I have about the transformation and ...
3
votes
3answers
142 views

How can I assign matrix values in below form? [closed]

I want to create matrix as the below fig. shows. How can I do it with a do-loop, for-loop, if-loop, or any other way? Thanks a lot...
2
votes
1answer
57 views

Efficiently Invert a Square, Block Diagonal Matrix

I am generating an n x n matrix where n is specified by DIM: ...
9
votes
0answers
158 views

Bug in PositiveDefiniteMatrixQ?

Fixed in 10.1.0. Exists in at least 9.0.1 -- 10.0.2. This seems like a bug in PositiveDefiniteMatrixQ to me: ...
3
votes
1answer
55 views

Extending matrix (x,y-axis + data) via Interpolation. Looking for elegant & efficient way to write

Please, feel free to edit the title, if necessary. Hi, this is my code working, but actually, the size of my real dataset is 100x100. So, this is very inefficient way. What would be the most ...
1
vote
1answer
79 views

Replacing negative components of a matrix with zeros [closed]

How can I replace the negative components of a matrix with zeros?
0
votes
0answers
23 views

Finding the percent difference between elements of a matrix and a list/vector [duplicate]

I have a large matrix of 24 columns, 11 rows, and a vector in the form of a one column, 11 row table. What would be the best method of finding the percent difference between each element of the matrix ...
1
vote
4answers
146 views

Non-rectangular pick of elements of a matrix

How to pick elements of a matrix that are inside a circle centered at the center of the matrix?
3
votes
1answer
152 views

How can I optimize the search between two lists, one that is changing length?

I'm trying to identify unique arrays by comparing two lists, one which is growing in length. The number of elements in the list grows as 2^n^2, where ...
3
votes
2answers
136 views

Summing matrix products

I need to compute a double sum over a weighted matrix product: $L[M]=\sum_{i,j}^{N}\Lambda[[i]]\;\omega[[i]].M.\omega^{\dagger}[[j]]$. $\Lambda$ is a list of with N complex values(weights) and ...
2
votes
3answers
138 views

How to write the Taylor expansion of the sum of several matrices?

When $A$ and $B$ are matrices, we have the following Taylor expansion for the inversion function together with basic information on convergence: $$ ...
9
votes
2answers
238 views

Why is Mathematica eating a row from QRDecompostion

I'm attempting to calculate the QRDecomposition of the matrix: a = {{1, 3}, {0, 5}, {2, -8}} QRDecomposition[a] The answer ...
4
votes
1answer
64 views

Creating a tensor from matrices

I have 3 nxn matrices that I'd like to combine into a nxnx3 tensor. Basically, I want a new nxn matrix where each element is a 3 tuple of the elements of the other 3 matrices at that same position. ...
3
votes
2answers
105 views

Matrix Diagonalization programming

I have a very simple problem, with me misunderstanding the use of Modules and Functions in general, in mathematica. I have a function of which I want to input a Matrix, and in the function I want ...
0
votes
0answers
87 views

How to Extract and Rearrange Elements in Doubly-Nested Lists

Hopefully any easy problem for you guys to help me with! I'm currently having an issue with writing some Mathematica code that will extract the each nth element in each array within a matrix, and then ...
6
votes
1answer
454 views

What does it mean when Mathematica returns a zero “eigenvector”? [closed]

For example, I ask Mathematica to compute the eigenvectors of $\left(\begin{array}{cccc} 1 & 1 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 5 & -4 \\ 0 & 0 & 4 & ...
1
vote
3answers
85 views

Percent Difference between elements from 2 matrices

If i have a 22 by 25 table of values which depend on n and r, and a list of values that depends on r that is a 22 by 1 matrix, how can I find the percent difference between each element, by row in the ...
9
votes
4answers
5k views

Matrix Multiplication in context of row and column vectors

I've been looking at some matrices in Mathematica and I've noticed something very weird: They're extremely temperamental when it comes to dot products! For example, if I have the following, ...
3
votes
2answers
155 views

Zigzag ordered encoding of DCT co-efficients

I am doing DCT steganography. I have obtained a matrix of DCT co-efficient. I now want to perform zig-zag ordered encoding. The matrix is as follows ...
6
votes
1answer
121 views

Issue in Det[…] when computing determinants of polynomials?

When I form a matrix of at least size $12 \times 12$ of second order polynomials in $w$ and I calculate the determinant of that, I get something that is a rational expression in $w$. Since the ...
0
votes
2answers
55 views

Plotting plane from a matrix or data table

After weeks collecting data I've decided to pass my results through Wolfram Alpha and see what it gets. The results are amazingly useful, specially the plane generated by linear regression. It is ...
3
votes
0answers
84 views

How to force Series[] to compute expansions by considering non commutative multiplication?

I wish to compute the Taylor series expansion of the following iteration method $x_{k+1}=x_k-f'(x_k)^{-1}f(x_k)$ up to four terms of error ($e_k=x_k-\alpha$). When this is a scalar iteration, I very ...
0
votes
1answer
44 views

Plotting results of 'Do' loop in contour graph

I want to plot the results of a 'do' loop as a contour graph: ...
4
votes
1answer
62 views

How to create overlapped block matrices and simplify the result

This is sort of a duplicate of Creating overlapped block matrices, but the question wasn't fully answered since the OP never returned to clarify. I am using Kuba's answer for FEM, but I have been ...
0
votes
1answer
56 views

Make Function from matrix [closed]

I have a set of excel data (time v temperature). When I extract it to mathematica it creates a matrix. I want to put the temperatures into a function that is time dependent, so is there a way to use ...
0
votes
1answer
127 views

Solving linear system with constraints

I need to come up with a solution for a rather, odd situation. Let's say I have an $M \times N$ matrix called ${\bf A}$, and I would like to solve it for ${\bf x}$ where $b_1 \le {\bf A} {\bf x} \le ...
1
vote
3answers
74 views

How to convert a matrix into a sparse matrix [duplicate]

If I have a matrix: row 1)1 0 0 4 row 2)0 0 0 0 row 3)5 1 0 0 row 4)0 5 0 0 row 5)0 0 0 9 How would I put it in a sparse matrix format: ...
5
votes
2answers
244 views

Speed-up the computation of this sum of small matrices

Given a matrix mat with a large number of rows (a few thousands) and a few columns (between 2 and 10), I'd like to compute the sum of the "small" matrices obtained ...
7
votes
1answer
90 views

A few tuples at a time?

I want to generate $n$ by $n$ binary arrays, and then reduce the output from those arrays by performing a number of permutations and eliminating duplicates. The problem is that the number of arrays ...
6
votes
2answers
506 views

Polar Decomposition

I'm new to Mathematica 10 (half-a-month user). I'm looking for a function of polar decomposition but for now I cannot find it. Can anyone tell me about related functions. Thanks in advance.
14
votes
6answers
427 views

Given a large binary matrix, find the largest submatrix containing non-zero elements

I'm looking for a way to reduce a binary matrix containing zeros at some positions into a matrix that contains no zeros by deleting rows and columns of the original matrix until only non-zero values ...
0
votes
0answers
44 views

Problem with stress transformation using InputField [duplicate]

I want to write a code for application of the transformation matrix onto a second-order stress tensor. I have a problem with showing the results. My steps are as follows: 1) I create a Grid with ...
1
vote
1answer
176 views

Transform list of inequalities into matrix form $A\ x \leq b$

I have a list of linear inequalities, and I want to get it into the form $A\ x \leq b$; i.e., find the matrix $A$ and the vector $b$. Is there any function in Mathematica that can that can do this?
-3
votes
1answer
47 views

Singular matrices with index 1 [closed]

If $A\in \mathbb{R}^{n\times n}$, the index of $A$ is the smallest integer $k$ such that $rank(A^{k+1})==rank(A^k)$ I want to find a singular (id est $\det(A) == 0$) and non symmetric matrix $A$ ...
1
vote
2answers
53 views

Importing data, then plotting ListPlot. What's the most efficient way to write a code?

It should be a boring question to ask for someone, but this is very basic need which I haven't resolved by myself. I know I can use MapThread and pure function to make it short and beautiful, but even ...
1
vote
1answer
95 views

How can I get symbolic orthonormal eigenvectors for 3 by 3 hermitian matrix?

Using the following syntax, I can obtain the symbolic eigenvalues and eigenvectors of the following Hermitian matrix (a,b,c,d are all real parameters): ...
9
votes
4answers
248 views

How to convert a sparse matrix to a list of sparse arrays?

I have a matrix stored as a SparseArray. How can I convert it to a List of its rows, where each row is stored as a ...
1
vote
2answers
73 views

Is it possible to draw a line on a MatrixPlot that would reflect density of row values? [closed]

I have a MatrixPlot with some data and I'd like to draw a vertical lines representing the "average" (density) of that data for each row. Something like this for ...
4
votes
0answers
169 views

Finding eigenvalues in Mathematica: why so slow?

I am trying to find the eigensystem of a large sparse real symmetric matrix, and I only need the lowest 40 or so eigenstates. The relevant code is as follows: ...
1
vote
1answer
95 views

diagonalization function

If we have a matrix m which is n*n, how can I do mm=U^dagger m U which is a transformation ...
6
votes
3answers
267 views

How can I create a random symmetric matrix in this way?

The most straight forward way for me to think about is like this: ...
6
votes
0answers
129 views

Why has Version 10.3 precision reduced?

In version 7.0.1.0 and versions 10.0 and 10.1 the following is produced: ...
1
vote
1answer
45 views

How to find selected elements of inverse of a banded matrix without inverting it?

Is it possible to find some selected elements of the inverse of a large sparse matrix without inverting it? For example consider this Hermitian matrix (as a general case). ...
1
vote
1answer
182 views

Derivative of a symbolic matrix

I need to write an elasticity equations as: {{a*∂/∂x,b*∂/∂y},{c*∂/∂x,d*∂/∂y},{e*∂/∂y,f*∂/∂x}}.{{u},{v}} where a,b,...,f are ...
0
votes
1answer
57 views

LinearSolve on non-square matrices?

I just came across a strange behaviour for LinearSolve (on Mathematica 8.0.0.0). Consider the following definitions: ...
1
vote
1answer
80 views

What's is the restrictions for the function MatrixExp?

When I use the MatrixExp on a general $2\times2$ matrix, Mathematica gives me this result: MatrixExp[{{a,b},{c,d}}] // TraditionalForm ...
9
votes
1answer
224 views

Speed up construction of a dense matrix

I wish to find the numerical eigenvalues of a relatively small (100 dimensional) Hermitian matrix. While the eigenvalue calculation itself is fast, the construction of the matrix is taking longer than ...
1
vote
1answer
55 views

Fast arithmetic on matrix elements

I have a square matrix $U$ of dimension $L\times L$, I am interested in the following quantity $U_{1,j}U_{2,k}U_{3,l}U_{4,m}\cdots U_{L,q}$ summed over all permutations of the letter indices, ...