Questions on the manipulation of matrices in Mathematica.

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-1
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1answer
50 views

Beginner Question: Assigning an indexed Variable to a given list

I am pretty new to the game and have a problem, which i am sitting on for hours. 1) I created a random Matrix 5x5 ...
4
votes
1answer
67 views

Speed up the auxiliary function magicSquare when $n$ is doubly-even

Today, I saw a question about magic square. Please see here When $n$ is doubly-even.Namely, Mod[n,4]==0 ...
1
vote
1answer
62 views

Divide each element of a list of 500 matrices by another matrix

Lets say that I have a Table of dimension (3,3,500) and I'd like to perform element-wise division by a 3x3 matrix along the third dimension (of length 500 in this case). What is the most elegant way ...
8
votes
3answers
651 views

The magic square function

There're some matrices that the sum of columns, sum of rows, and sum of diagonals are the same value. Here is an example: ...
1
vote
1answer
66 views

Assigning some results after a solve procedure to the coefficients of a matrix

I have a matrix M[3,3]. After a solve procedure, I obtained these results. {{M[1, 2] -> Cos[ψ[t]], M[1, 3] -> 0, M[2, 3] -> 0, Cos[θ[t]] -> M[3, 1], M[3, 2] -> 0, M[3, 3] -> 1, M[2, 1] -> ...
0
votes
0answers
33 views

Parametrizing a matrix given its trace and norm

I have a problem where I have to generate random matrices with the following properties: ($a$ is a given fixed number) $\mathrm{Tr}\, A=0$ $\mathrm{Tr}(A^\dagger A)=\|A\|_F^2=a$ I was wondering ...
4
votes
4answers
113 views

Express block matrix in terms of matrix basis

I'm trying to construct a function that returns the multiplication table of a matrix Lie algebra. Assuming a basis of matrices, my definitions: ...
-1
votes
1answer
91 views

Laplace equation

I tried to run this code, but it doesn't work for NDSolve ...
5
votes
4answers
173 views
2
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1answer
102 views

Anyone knows the algorithm used by NullSpace function?

NullSpace function gives a list of vectors that forms a basis for the null space of the input matrix. When the rank of the input argument matrix $M_{m\times n}$ is ...
4
votes
2answers
113 views

Gridding in a Nested Matrix

We have a nested matrix as: nested={{he, {{e, f, g, h}, {s, 0, q, i}, {s, 0, q, j}}}, {ho, {{e, f, g, h}, {0, u, t, i}, {u, t, 0, j}}}} and with the line ...
0
votes
0answers
54 views

Recursive computation using Piecewise

I am trying to create an array using a series of equations using Piecewise. I am stuck in one of them. I am just putting a simplified version of code as below. I ...
4
votes
4answers
708 views

Writing a circular matrix

I have two square matrices, $A$ and $B$, of the same size, say, of $m \times m$. What I want is to write a programme/function of three variables, $A$, $B$ and $n$, that outputs the $mn \times mn$ ...
0
votes
0answers
36 views

Deciphering output messages using Solve

I'm trying to solve the following system. The error messages I'm getting suggest that there may not be a solution [my desired result], but I'm not sure if there could be something else going on. The ...
0
votes
0answers
55 views

How to handle substrings of a matrix by a named index

I am using open source code to run stochastic simulations. The output looks like this: ...
1
vote
3answers
96 views

Absolute VectorPlot scaling

I'm trying to visualize the vector components of a rotation matrix with absolute vector lengths. VectorScale help states that When using an explicit sfun, ...
1
vote
1answer
94 views

Getting a part of a matrix Inverse for later use

I was trying to get an element of a matrix, and use in further computation of my program. Problem was that its not reading the value unless and until I specify it again. My code is: ...
3
votes
2answers
270 views

How to rewrite this function to be faster: Find sub-matrixes of boolean board which imply a given boolean pattern

I have Boolean matrix A (called "board") and Boolean matrix B with smaller dimensions (called "pattern"). I am trying to find sub-matrixes C of A such that C has same dimensions as B, and ...
0
votes
0answers
66 views

Matrix iteration failing after second step

I am calculating 11x6 matrix using different logics as in below code. Problem is in Do loop in below code where I have two different criteria to update matrix "fd". I am expecting logic in IF which ...
0
votes
1answer
49 views

Replace element of matrix based on rule which invloves other element of same matrix

I am trying to replace 1s row of matrix d iteratively from right by multiplying last element in 1st row with (1-int*dt) to generate 2nd last element. The replacement continues till I reach the 1st ...
0
votes
0answers
54 views

How to replace a part of array based on certain rules which involves usage of other array

I am trying to replace outermost column of array "fd" in below code. fd is matrix of dimension (nas1,nts) which is initially filled with 1. I want to replace outermost column of fd with result of Max ...
28
votes
2answers
731 views

eigenvector bug?

Bug introduced in 7.0.1 or earlier and fixed in 10.0.0 I have a fairly simple $3\times3$ complex matrix, $$ M=\left( \begin{array}{ccc} \frac{7}{2}-\frac{i}{2} & -1+i & \frac{1}{2}+\frac{5 ...
2
votes
1answer
71 views

Abstract iterator in Do

I'm trying to write a module. Its input is a matrix (tensor), the module should return new tensor with increased rank with 1. The new tensor is defined as $$ O \Rightarrow N_{\alpha \beta \ldots ...
1
vote
2answers
69 views

Problem in matrix multiplication

I created a random directed acyclic graph using Mathematica. I need to compute a specific function from its adjacency matrix. ...
2
votes
2answers
166 views

Are there any good mass row/column swapping functions for matrices?

I have the following matrix Keeping the 20 row and 20 column fixed (so the 21st rows and columns because I started at 0)...how do I push each row and column back one spot? I need to push the 0th row ...
1
vote
3answers
210 views

Writing code to update a large matrix?

How can I write a code to update a matrix based on certain rules? I plan on constructing a large matrix, and I cannot submit entries one by one. The rules for the matrix are as followed: $$ ...
1
vote
1answer
102 views

How to add an extra column to a current matrix (list)? [duplicate]

a = {{-800, 1712}, {-801, 1713}, {-806, 1832}} TableForm[a] b = a[[All, 2]] - Min[a[[All, 2]]] How do I make a new matrix (list) whic looks like this ...
2
votes
1answer
98 views

How do I generate all $n\times m$ matrices s.t. $a_{i,j} \in {a … b}$?

Is there a fast and clean way of generating all possible $n\times m$ matrices s.t. $a_{i,j} \in \{a ... b\}$ - much like Range does in $N$? Consider for example that for $n,m = 2$, $a=0$, $b=2$ I ...
1
vote
0answers
28 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): ...
-2
votes
1answer
80 views

Recreating in Mathematica a matrix created in Python [closed]

I need to recreate in Mathematica this matrix that I created in Python: ...
0
votes
1answer
55 views

Plotting six chosen rows of a matrix

I have a matrix,W, whose dimension is n x n, each entry is a number. I need to plot only the values of six rows, namely those ...
0
votes
1answer
73 views
1
vote
2answers
95 views

Filing matrix by bands [closed]

I need to fill a matrix, CSI, by taking elements from an array, inverse, which is the Inverse Fast Fourier Transform of an array ...
2
votes
1answer
59 views

sparse array with list [closed]

i'm trying to populate a sparse array with lists in certain positions, i tried the following code, ...
1
vote
2answers
54 views

How can I manipulate this list?

I performed a loop with Table where I solve a system of 4 equations that depends on two parameters: eta and p. I create two lists for each parameter as follows: ...
1
vote
1answer
68 views

Defining a function of matrices [closed]

I am translating my code from Python to Mathematica. How can I define a function similar to the following: ...
0
votes
3answers
79 views

Define a matrix depending on variable in Mathematica [closed]

I am translating my code from Python to Mathematica. I am trying to define a matrix, whose values depend on a variable chosen by the user, called kappa. In Python the code looked like that: ...
1
vote
4answers
104 views

calculating subsets of a matrix (L=40X40)

I need to calculate all $k$-possible subsets$(k:1,L)$ of matrix with size $L$. I am using subset function as following, ...
0
votes
1answer
58 views

What is the “proper” way of multiplying a list of vectors by a matrix? Why Map does not work? [closed]

I am an absolute newbie with Mathematica, so please forgive me if this is stupid, but for the life of me I can't solve this. Suppose I have a list of vectors $b_{1...n}$ and a square matrix $A$ and I ...
15
votes
5answers
3k 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 ...
28
votes
4answers
3k 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 ...
4
votes
3answers
136 views

Unragging a matrix

Today I ran into matrices like this one: ...
2
votes
3answers
136 views

How to insert a Matrix into a larger matrix

I have a 4x4 matrix v1 v2 v3 v4 myM={{a1,a2,c1,c2}, v1 {a2,a3,c2,c3}, v2 {c1,c2,d1,d2}, v3 {c2,c3,d2,d3}} v4 And I want to ...
0
votes
0answers
40 views

How to add a positive definiteness of a unsymmetric matrix as a constraint to a Findminimum problem

The problem is I have a function which has 33 variables, and which to minimize it in a given set of contraints. I have also a matrix consisting of these 33 variables. The condition is that this matrix ...
0
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0answers
9 views

Add positive definite matrix constraint to an optimization problem [duplicate]

The problem is I have a function which has 33 variables, and which to minimize it in a given set of contraints. I have also a matrix consisting of these 33 variables. The condition is that this matrix ...
8
votes
0answers
123 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: ...
0
votes
1answer
55 views

Maximum element and its position (row,column) of matrix

Can someone help me to get the maximum element of $m\times n$ matrix and corresponding row and column $(i,j)$?
1
vote
1answer
63 views

Counting and updating a subset of matrix

I have an n by n matrix and would like to count the number of sub-matrices that is equal to a given matrix. Here is my code: DWBCL creates a matrix with elements a1, a2 and c2 in it and DWBCH with b1, ...
1
vote
2answers
54 views

Filling a matrix with a list of lists

I have a list of lists with different lengthes: {{a1,a2},{b1,b2},{c1,c2,c3},...} Now I want to create a matrix the following way: ...