Questions on the manipulation of matrices in Mathematica.
4
votes
3answers
116 views
Compute the rank of a matrix with variable entries
Say I have a matrix like
$$
M=\left(
\begin{array}{c c c}
x & xz & w-2x \\
wz^3 & xy & z \\
y^2-z^3 & x+w & z+x^5
\end{array}
\right)
$$
is it possible to ask Mathematica ...
1
vote
2answers
93 views
Matrix echelon/upper diagonal form
Is there a way to find the echelon form of a matrix in Mathematica? I see there is a function to find the reduced echelon form, RowReduce[], but I can't see ...
0
votes
0answers
81 views
Defining and Solving Systems of Equations Using Matrix Tables
I've defined a system of equations, but I been unable to get Mathematica to solve for the individual variables created by matrix tables.
...
1
vote
0answers
89 views
Dynamically filling matrix with a[[n,m]] = 1/a[[m,n]]
I'm building a square matrix, with 1s on the diagonal and elements in U the inverse of elements in L, which are random integers drawn from the sequence 1, ..., 9. Given the nature of the problem I ...
1
vote
2answers
273 views
badly conditioned matrix (General::luc)
With some matrices I am receiving the following message
Inverse::luc Result for Inverse of badly conditioned matrix (M) may contain significant numerical errors.
How can I tell to Mathematica to ...
-4
votes
2answers
80 views
Ploting from Matrix [closed]
I use Import function from excel in order to get my data. My data contains 3 columns.
...
2
votes
2answers
70 views
changing a symbol into a function variable
Struggled for a while on this problem and hopefully you can help... I have a mathematical expression that currently has a symbol where I used to have a function variable. How do I make the symbol ...
7
votes
2answers
163 views
Why does my matrix lose rank?
I want to check the rank of a matrix for observability, but Mathematica loses a rank if the matrix contains very large numbers.
Let's say my matrix is
...
9
votes
2answers
221 views
How to extract and compute on the diagonal entities of a sparse matrix very fast?
As could be seen in the following code:
...
1
vote
2answers
111 views
Computing distance matrix for a list
Using functional programming in Mathematica, how can I compute a distance matrix for every element in a list of matrices... The distance would be computed between the item in the list and a "target ...
11
votes
1answer
457 views
Eigenvalues and Determinant of a large matrix
Can anybody kindly explain to me what is going wrong regarding a simple problem I have? I can find the eigenvalues of a large matrix using Eigenvalues[], but when I ...
6
votes
5answers
197 views
Is there a built in function to obtain the back diagonal of a matrix?
Given the following matrix:
m = Array[Subscript[a, #, #2] &, {4, 4}]
how can I find the skew diagonal or anti-diagonal or back diagonal of the matrix ...
0
votes
1answer
925 views
Quick Hessian matrix and gradient calculation?
I am absolutely new to Mathematica and I actually want to try implementing a little optimization method .
Long story short assuming I have a predefined two-variable function f(x,y) I want to ...
1
vote
1answer
96 views
Weighted Kirchhoff Matrix?
I have a weighted graph and I want its graph Laplacian matrix (what Mathematica calls the Kirchhoff matrix in the unweighted case). Is there an easy way to get this?
For example, the command:
...
4
votes
2answers
628 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:
...
1
vote
2answers
146 views
Efficient ways to create matrices and solve matrix equations
I am attempting, for the first time, to use Mathematica to do some serious linear algebra. I would like to solve systems of equations of the form $$U_{n n'} f_{n'} = b_n.$$
I have an expression for ...
0
votes
0answers
119 views
6x6 matrix NullSpace
I'm working with a 6x6 matrix. Whenever I try to find the NullSpace and FullSimplify it, I get the error
No more memory ...
0
votes
0answers
18 views
Symbolic Calculations with formal matrices [duplicate]
I want to make calculations with matrices in the form (for lovers of statistical mechanics, is just the first step replica symmetry breaking)
...
-7
votes
5answers
213 views
Translating MATLAB's cell2mat into Mathematica
How I can define a function in Mathematica such that it acts same as the cell2mat command in MATLAB?
Example (in MATLAB):
...
3
votes
0answers
65 views
Is it possible to lower the bitwidth of (floating point) numbers?
The answer to this question will most probably be a definite no. Nevertheless, I would like to know whether it is possible to represent reals in the memory on less than the standard 32 or 64 bits ...
-1
votes
2answers
84 views
Convenient methods to sum select rows (or cols) of a matrix? [duplicate]
What are some convenient methods to sum selected rows or columns in a matrix? This question Summing along rows or columns of a matrix only addresses how to sun entire rows or columns ie, by level.
...
4
votes
1answer
66 views
Using the mouse coordinates to index a matrix
I would like to "write" on to a matrix using the mouse. That is, I would like to use the integer value of Locator coordinates (p) to index a matrix. Then, if the mouse button is down, write a 1 in ...
0
votes
2answers
189 views
How to get complement from two matrices?
This is a special case of my question How to do nor on matrices?
...
1
vote
3answers
109 views
Define new number set
May seem strange at first, but can you make mathematica change the value of 0 to 10 and 11 to 1 for all occurrences. Let me explain:
I'm looping through a matrix and for each element, I want ...
0
votes
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 ...
1
vote
2answers
93 views
How do I divide the columns of a matrix by the sum of its elements?
I am trying to create a transition matrix for a network. In order to do this, I need to sum down the column (the out degree), and then divide the column by the out degree in order to normalize it.
...
0
votes
3answers
157 views
Matrix Determinant
I have an N by N (N>3) matrix generated from fortran. I would like to find determinant of that matrix using mathematica? I could do this for a 3 by 3 matrix. I can also import the fortran output file ...
9
votes
2answers
627 views
Solving a time-dependent Schroedinger equation
I want to solve the time-dependent Schroedinger equation:
$$
i\partial_t \psi(t) = H(t)\psi(t)
$$
for matrix, time-dependent $H(t)$ and vector $\psi$.
What is an efficient way of doing this so ...
-2
votes
1answer
88 views
Fortran kind of matrix creation [closed]
I want to create the matrix H of dimensions nxn and matrix elements H(i,j). Because of the physical problem I am dealing with, it is necessary to build it in the following not trivial way.
I know how ...
1
vote
3answers
138 views
Convert coefficients of polynomials into a matrix
I have several sets of 5 polynomials of the form:
...
0
votes
1answer
101 views
Get value only from Position
If have the following command
Position[{a, b, a, a, b, c, b}, b]
(* Out[1]= {{2}, {5}, {7}} *)
Is it possible to get only a sequence of values instead of this ...
6
votes
3answers
165 views
Permanent minors
The function Minors yields the minors of a matrix. Is there a function that yields the permanent minors of a matrix?
3
votes
1answer
234 views
Efficient method for inverting a block tridiagonal matrix
Is there a better method to invert a large block tridiagonal Hermitian block matrix, other than treating it as a ordinary matrix?
For example:
...
7
votes
2answers
166 views
How to generate a matrix group?
I have three $7\times 7$ matrices (with real entries, lots of zeros) and I'd like to check if they generate a finite group (or, more precisely, if the group they generate is of precise order). Would ...
1
vote
1answer
60 views
Is there a cleaner/shorter way to select-replace in matrices? [duplicate]
I love Mathematica, but I find it oddly lacking when it comes to how matrices are handled. Here is an example of code that works but seems like it should be a lot shorter (and minus the loop).
I'm ...
0
votes
0answers
65 views
Mapping a function to a Matrix [closed]
I’ve looked up previous answers to this question but haven’t found a suitable answer.
I am trying to Map a function that I defined across a Matrix. The function Maps fine across a 1D array but can’t ...
9
votes
2answers
210 views
Speed up 4D matrix/array generation
I have to fill a 4D array, whose entries are $\mathrm{sinc}\left[j(a-b)^2+j(c-d)^2-\phi\right]$ for a fixed value of $\phi$ (normally -15) and a fixed value of $j$ (normally about 0.00005). The way ...
0
votes
1answer
102 views
2
votes
1answer
43 views
Replace a specified portion of an array with elements from another smaller array
This may be a trivial question, but I have been at it for a couple of hours and I have not made much progress.
I have a 10 x 10 array (T) that I have used to generate an 8 x 8 array (Q). I want to ...
0
votes
1answer
65 views
Why does Eigenvalues[matrix I defined] not work? [duplicate]
This is the code I have in my mathematica notebook. I want to find the eigenvalues of the matrix I created called Hmatrix as defined below. However when I type Eigenvalues[Hmatrix] I get the Hmatrix ...
-1
votes
1answer
124 views
An issue regarding Eigenvalues function [closed]
Can anybody please kindly explain to me why the members of the output vector produced by the following example are not equal to zero?
...
3
votes
1answer
141 views
How to get the determinant and inverse of a large sparse symmetric matrix?
For example, the following is a $12\times 12$ symmetric matrix. Det and Inverse take too much time and don't even work on my ...
1
vote
3answers
186 views
How do I create a matrix of functions?
I'm trying to create a matrix in which the elements are functions of two variables, but I can't figure out how to do it. Is it possible? The only way I could figure out is to define the matrix in ...
1
vote
1answer
91 views
Importing a matrix from a text file
I have a $4 \times N$ matrix in a .txt file of the form:
-17.071 137.567 16.554 0.65
-16.873 136.138 16.934 0.7
-15.397 135.738 16.894 0.7
-14.7 135.982 15.9 0.6
...
2
votes
1answer
146 views
Solving an equation involving a determinant
I have a matrix which doesn't include numerical values. There are four variables in it. It is defined by
...
4
votes
2answers
232 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 ...
4
votes
1answer
327 views
TensorContract of inverse matrix
Matrix inverse in mathematica
If $A$ is an invertible $n \times n$ matrix, then $A\cdot A^{-1} = I$.
To get this statement in Mathematica, you need the assumption
...
19
votes
1answer
922 views
Is there a way to convert an image into a Graph?
I'm trying to convert an image with several overlapping dots into a Graph. The goal is to be able to derive the Kirchhoff matrix for the randomly created "network ...
1
vote
1answer
66 views
Confirming the existence of a function related to a matrix
Is it possible to get an answer to the following question in Mathematica?
Let $M$ be a $n$ by $n$ matrix, is there a function $m:\mathbb{N}\times \mathbb{N}\rightarrow \mathbb{Z}$ such that ...
4
votes
2answers
150 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 ...
