Questions on the manipulation of matrices in Mathematica.

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1
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1answer
108 views

Unexpected inefficiency when calculating matrix product by Dot

There is an unexpected inefficiency when I calculate matrix product by Dot. The only relevant part of my code is presented as follows: ...
14
votes
1answer
425 views

How do I create a triangulated surface from points?

I have a set of points in a nx3 matrix and I would like to convert them into a surface, so that I may calculate its surface area. The function ListSurfacePlot3D creates the surface how I want it. ...
0
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0answers
85 views

Null space of a stochastic matrix [closed]

I want to calculate NullSpace of a matrix m - IdentityMatrix[n]. Normally I would do it with ...
3
votes
2answers
239 views

Matrix Plot: How to Apply color function to only a region of the plot

I want to make a matrix plot where a color function is applied to a region of a matrix. Those matrix elements which were not in the region specified should not have any color associated with them, and ...
4
votes
2answers
218 views

Pauli matrices — simplify expressions without printing out the raw matrix

Squaring a Pauli matrix results in the identity matrix. These bits of documentation (weakly, to a Mathematica-newbie like me) imply that some algebraic identities that link the Pauli matrices ...
3
votes
2answers
3k views

Is there a built-in function to find the adjoint of a matrix?

I've been looking for a function that helps me get the adjoint matrix o a given one, I found that you can get the cofactors of a matrix but only by using the "Combinatorica" package, which I couldn't ...
15
votes
1answer
664 views

How get eigenvectors without phase jump?

I'm using Eigenvectors to get the eigenvectors for some matrixes, but the eigenvectors seems to have some phase jump. Here is an example: Say we have a 2 by 2 ...
0
votes
0answers
37 views

Why is there a different eigenvector for the same matrix? [duplicate]

I have a matrix that depends on two variables x and y. Matrix[x,y] When I make x=-.25*(1 - 1/3) + .25*(1/3) + .25 y=0 I ...
1
vote
1answer
74 views

How to specify positions in a matrix by an array?

If I have an array of sets of points such as pts = {{2,4},{1,3},{5,7}} Is there any super short command to use those pairs to output their respective elements in ...
2
votes
5answers
243 views

Add values from a list, at positions from a list, to a matrix

I'm investigating matrix assembly and one of the things I'm trying to do is add specific values to a larger matrix based on a list which is essentially defining connectivity of nodes. For example: ...
0
votes
1answer
112 views

How do I store Eigenvalues of a 14*14 matrix in a For loop into an array and then plot that array? [closed]

I have a matrix 14*14 that is dependent on parameter a. How can I plot eigenvalues of the matrix according to varous values of a?
7
votes
5answers
1k views

Check if a matrix is Positive Semidefinite

I have a question concerning the check whether a given matrix is positive semidefinite or not. In mathematica the function PositiveDefiniteMatrixQ[m] tells me ...
0
votes
0answers
173 views

Normalized, symbolic Eigenvectors without abs(), sign() etc

I'm trying to compute the normalized eigenvectors of a matrix M = {{0, 0, 0, 0}, {0, 0, M5, 0}, {0, M5, 0, M4}, {0, 0, M4, 0}} If I try Normalize ...
0
votes
0answers
48 views

vector product defined on kronecker delta [duplicate]

I have some vectors such as : a={{0}, {0}, {0}}; b={{1}, {1}, {1}}; c={{1}, {1}, {0}}; I wanted to product a by ...
2
votes
1answer
61 views

formatting matrix

I have imported a matrix from data file which was generated in Matlab. The problem is the character (") in beginning and end of every row. So I can not perform any operation on it. How to get out ...
4
votes
1answer
204 views

Eigenvalues of matrix not giving imaginary parts

This might be a very simple problem, but I can't seem to figure out why I am getting this. I am trying to find the eigenvalues of the matrix: ...
0
votes
0answers
69 views

Operatorial matrix

Suppose I have a matrix M=$\begin{pmatrix} A(p) & B(p) \\ C(p) & D(p)\end{pmatrix}$. I want to apply some operatorial matrix E such that EM=$\begin{pmatrix} 0 & \partial_p & \\ ...
3
votes
1answer
68 views

Recognising degenerate maxima in a matrix

Say I have the following matrix $\left( \begin{array}{cccccc} 1. & 0 & 0 & 0 & 0 & 0 \\ 0 & 0.707107 & 0 & 0 & 0 & 0.707107 \\ 0 & 0.707107 & 0 ...
0
votes
1answer
55 views

Designing a loop that fetches 5 random vectors each with 5 components from a set of 10 until Linear dependence is found

I am currently trying to find a way to make a loop that will select 5 random columns without replacement of a 5x10 matrix until it finds a determinant equal to 0 out of the new matrix formed by the 5 ...
2
votes
1answer
570 views

Matrix exponential MatrixExp[] vs Sum[MatrixPower[]] doesn't match?

I might be an idiot, but I cannot get the manual expansion of $e^{At}$ to match the MatrixExp[A t] result. For example, I have the following: ...
1
vote
0answers
144 views

Replace part of a matrix

I have to generate a ne numbers of matrices with 1 and 0 and then replace some elements. ...
14
votes
2answers
3k 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 ...
0
votes
1answer
91 views

Problem with writting into a matrix in Mathematica [closed]

I have declared a matrix using S = ConstantArray[0, {246,246}] And when I try to write into it by a loop I get the following error "Tag Times in 0\ Null is ...
2
votes
1answer
237 views

Rearranging a biclustered matrix

I currently have a $77\times 38$ matrix, and I have used a clustering algorithm to cluster the row data and column data. The rows and columns of my matrix correspond to a list of country codes (not in ...
2
votes
3answers
206 views

Efficient matrix multiplication

I have a list of vectors vecs = {vec1, vec2, ..., vecN} where veci is a list with length $N$. Now I have a matrix $N\times N$ ...
1
vote
3answers
163 views

Randomly changing matrix entries

Write a block of code that generates a 4x4 matrix with randomized real number entries each between 0 & 1, then selects 3 matrix entries at random, and finally replaces these 3 entries with ...
1
vote
1answer
196 views

Transform linear system into a matrix form

I have a system of linear equations in variables $A_n$ of form: $$ \sum _{k=-K}^K h_k A_{n-k} J_{n-k}\left(\frac{(1-i) \text{$\eta $Sqrt}(n-k)}{\sqrt{2}}\right)+A_n\left(\frac{(1-i) \eta ...
-1
votes
1answer
189 views

Strange bug involving a list, “Objects of unequal length” [closed]

sortedTally is a list generated from Tally sortedTally[[1]][[1]] is a list If I print: ...
3
votes
1answer
444 views

Plot 3D boolean Array or matrix in Mathematica

I have been attempting several methods to plot a 3D diagram of a n by n boolean array in Mathematica but none of them produced satisfactory result. I want the $3D$ plot to have a cube when ...
0
votes
1answer
98 views

How to count column occurrences in a matrix?

I have a matrix of data, and I want to count the number of columns that match, and have some way to organize them by frequency. But I don't want to count the entire column, but consider the matrix ...
1
vote
1answer
182 views

Why does Mathematica add Hold to the result of my user defined symbol?

In the code below I have defined a symbol that multiplies two block-matrices (I can't use the builtin Dot since Dot assumes that the matrix coefficients commute): ...
8
votes
2answers
871 views

Defining quantum-mechanical Bra and Ket operations

I have the following ket in the Fock basis: $\vert3, 0 ,1\rangle$, where each entry defines the number of photons in a particular mode and can take any one of the following numbers: 0, 1, 2, 3. As a ...
0
votes
1answer
93 views

whats wrong when I use for loop for creating a matirx? [closed]

When I use separate value for "i" and "j", I got the correct desirable answer. a = 2; i = 3; j = 3; !(*SubscriptBox[(matrix), ([([a])])]) = {{1, 1, 3}, {7, 4, 7}, {2, 6, 8}}; value = ...
2
votes
1answer
138 views

How to swap tensor indices without permutation?

Say I have a tensor of rank R, How to swap $i^{th}$ and $j^{th}$ tensor index? I do not want to use TensorTranspose because it requires to write down the entire permutation, i.e. ...
4
votes
1answer
185 views

Proving positive definiteness or semi-definiteness of a matrix

I have the following 4x4 real symmetric matrix: $K=\begin{bmatrix}3-3w & -\frac{4}{3}+a+2w & \frac{5}{12}+b-\frac{w}{2} & 0\\ -\frac{4}{3}+a+2w & -1-6a-3x & ...
4
votes
1answer
562 views

Principal Components - how to obtain linear transformations?

I have a list "xlsf" with 6 columns and 1200 rows for PCA analysis. The PrincipalComponents[xlsf] gives the following: "The principal components of matrix are ...
3
votes
1answer
289 views

Spectral Clustering

I am attempting to implement a spectral clustering routine using Mathematica, but I am encountering difficulties. Using the standard Gaussian similarity function found in section 2.2 of this paper ...
8
votes
3answers
561 views

Plotting triple data points while xy data are not regular

I plotted recently some figures in Matlab and their quality was not that satisfactory, so I come to Mathematica as my supervisor suggested. This is how such figure looks like in Matlab: . In Matlab, ...
10
votes
1answer
347 views

Drop selection of columns from a ragged array

I have an application where I need to drop some arbitrary list of columns from a ragged array (where of course the shortest array rows have at least all the specified columns). E.g., given a ragged ...
8
votes
2answers
657 views

Is there any fast way to solve a quadratic matrix equation in Mathematica approximately?

Let the square nonsingular matrix $M$ is a given convergent matrix. What are the best scalar values for $\alpha$ and $\beta$ (in the real numbers domain), at which the following quadratic matrix ...
4
votes
2answers
214 views

Improve simulation speed using Compile

I have two square matrices, a hermitian matrix h and an unitary matrix v. I am interested in the following function ...
0
votes
1answer
101 views

Creating Matrix,Inverted and Upper Triangulate inside Module

I was trying to fit this into a module but I didn't have any luck. And for some reason it won't Inverse the Matrix. Here's the code: Input: ...
108
votes
7answers
34k 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 ...
-1
votes
1answer
69 views

Help needed with assignment [closed]

Can I get some help with this: Write a module which as an input receives two matrices, the first matrix transforms in to the same matrix, but in the new matrix occur absolute values of the first, ...
6
votes
2answers
979 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: ...
0
votes
0answers
68 views

Which method to use for finding maximum without actually computing optimization function explicitly?

I am new to Mathematica and I am currently working on an optimization problem. The optimization function that I have easy to calculate for some assignment of variable but it is very difficult to ...
-1
votes
1answer
105 views

Module whose input is a function of 2 variables [closed]

I need to make a Module whose input is a function of 2 variables and 2 variables m,n so i can make a Matrix with Array. Basicaly, I need this: ...