Questions on the manipulation of matrices in Mathematica.

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3
votes
3answers
315 views

Matrix containing ellipse

I have to make a matrix which contains elements in an ellipse shaped region, but I need to make ellipse region in such a way that larger axis of ellipse is inclined with angle θ with horizontal. With <...
3
votes
2answers
262 views

Weird behavior when changing parts of matrix

I have this matrix: mat = {{1, 2, 3, 4, 5}, {6, 7, 8, 9, 10}, {11, 12, 13, 14, 15}, {16, 17, 18, 19, 20}, {21, 22, 23, 24, 25}}; and here are its second row ...
11
votes
9answers
768 views

Forming an upper triangular matrix from the elements of a list

I asked this question before, but i was closed because it the question was not comprehensible enough. So i reworded it, hope that's ok. I have a list with 6 elements. ...
1
vote
2answers
47 views

how to extract a matrix and a vector from a vector [duplicate]

I have a vector like this: V = {a*exp1+b*exp2+c*exp3, a*exp4+b*exp5+c*exp6, a*exp7+b*exp8+c*exp9} and I want to get : ...
1
vote
3answers
491 views

Finding maximum value with position from Table of values

I have this table of values, how do I find the maximum value? i.e. find $z_{max}(x,y)$ ...
3
votes
0answers
564 views

Symbolic matrix calculus: What's new in Version 9

I have seen some of the related posts, which ask about doing matrix calculation on tensors unknown dimensions. One of the posts mentioned that version 9 has some capability, but it was concerned about ...
8
votes
4answers
641 views

Fast method to select matrix elements based on a vector of positions

There is an operation for which I have long wanted to find a better solution. Let: a be a matrix of dimensions $m\times n$ v...
2
votes
1answer
125 views

How to solve an operator form of an integral equation by iteration method?

How I can obtain the $n^{th}$ approximation of the following Operator form integral equation? $F(t)=A(t)+\int_0^tds B(s)F(s)$, where $A(t)=\bigg{(}\begin{matrix}t&0\\Cos(t)&1 \end{matrix}\...
4
votes
1answer
221 views

How to input and output partitioned matrices that show partitions and compute as normal?

I want to demonstrate multiplication of partitioned matrices as in the example here. Using the Insert Menu, you can build a matrix and draw lines between rows and columns. However, I want to be able ...
1
vote
3answers
69 views

Collect the lists

I have a list of lists from which I pick out the positions of the number 1 and then print out these positions for each list. I am having some trouble collecting what I am printing into a list / matrix ...
2
votes
1answer
512 views

Why won't Mathematica obtain eigenvectors for this symmetric matrix?

The matrix is a real symmetric 4x4: ...
3
votes
2answers
303 views

Binarizing a matrix

I have an image with a few bright pixels with the remaining ones very dark. The difference is in orders of magnitude. I want to binarize this matrix (corresponding to the image) making all values ...
3
votes
3answers
207 views

Speeding Up Replacing of Labels in Large Matrix?

I am Mathematica novice and am trying to find a fast way to replace labels in some rather large matrices (512x512 or 1024x1024) that have resulted from segmenting images with WatershedComponents or ...
1
vote
0answers
63 views

deleteduplicates Delete elements of a list [duplicate]

I have a math problem about Mathematica, I am looking help from you. I hope that you could help me. The Math Problem: list= { {0,0,1},{1,0,0},{0,1,0} ,{1,2,3}}; ...
2
votes
4answers
976 views

How to plot a graph from it's incidence matrix?

I'm using Mathematica v9 and am trying to draw a graph by using it's incidence graph, but it won't draw it, which occurs an error "is not a valid incidence matrix.". But I've checked my matrix, and it'...
4
votes
2answers
292 views

All possible pairs of two items

I have 4 different items {1, 2, 3, 4}. I want to obtain all possible pairs of two of the items. I have written: ...
1
vote
2answers
222 views

Is there an easy way to divide a matrix into four blocks?

I often get a data table with column names and row names. For example: ...
3
votes
4answers
164 views
1
vote
1answer
150 views

Inverting matrix of unknown size

I have a matrix that has a variable number of columns and rows (but it is always square). The matrix is: $$ \Gamma = \begin{bmatrix} \Theta & 0 & 0 & 0 & T & 0 & R_j \\ ...
8
votes
8answers
761 views

Replace interior of matrix with zeros

I have f.e. the following square matrix: ...
10
votes
3answers
1k views

How to estimate the matrix condition number in the 2-Norm?

The Mathematica documentation says it is possible to estimate the matrix condition number in norms 1, 2, and ∞. But the 2-norm raises a message. This is an extract from reference documentation "...
1
vote
1answer
347 views

LinearSolve failing to find solution to system of linear equations of 64 variables

I've got a 64x64 Matrix L for which I want to find the solution to the matrix equation L . x == rho. L is defined as ...
0
votes
1answer
123 views

How to track row swap in Gaussian elimination?

How do I track which rows were swapped in the Gaussian elimination using RowReduce? I am doing metabolic control analysis on a mathematical of the energy metabolism I have in Mathematica. I need to ...
0
votes
0answers
106 views

Geometric Transformation not working - degenerate points?

I've successfully used FindGeometricTransformation to project the simplex triangle onto the x-y plane: ...
1
vote
2answers
246 views

Generic Matrices

A multivariate Gaussian distribution for $k$ dimensions looks like this: $$\frac{1}{\sqrt{(2\pi)^k|\mathbf \Sigma|}}\mathbf e^{ -\frac 1 2 \mathbf x^T \mathbf \Sigma^{-1}\mathbf x }$$ $\mathbf x$ ...
2
votes
1answer
216 views

Checkbox Matrix

Is it possible to create a dynamically changing binary $n \times n$ matrix $A$, which appears to the user as a $n \times n$ matrix/table of checkboxes and the user can change the entries of $A$ by ...
0
votes
2answers
78 views

solving series of matrices by simply multiplication

I have a number of matrices {2*2} containing element in series ....so by what method I solve that ... ...
7
votes
2answers
353 views

How to get rid of nested matrices

If I type into Mathematica TensorProduct[IdentityMatrix[2],IdentityMatrix[2]] It gives me a result that has nested matrices. How do I turn that into a normal ...
4
votes
3answers
237 views

How can I reproduce the MatrixForm, NumberForm, XyzForm behavior?

I wish to write a function like MatrixForm, that affect only display but not evaluation, i.e. a function that automatically is stripped away from output. More ...
1
vote
1answer
113 views

references in a nested matrix

I have a nested matrix n: ...
19
votes
11answers
1k views

Efficient way to build a certain square matrix

For odd n I'm looking for a short and swift way to construct with (f.e.) n = 3 n = 11 ...
15
votes
1answer
684 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 ...
-5
votes
2answers
226 views

Output of mathematica. Quaternion to Matrix [closed]

If I have the following instructions: How will it be the output/how will it appears in Mathematica? something like this: I can't recognize the output in mathematica... How can I do to appear ...
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: ...
1
vote
0answers
170 views

How to sequentially select, from a large set of tuples (of matrices), those with a certain property [closed]

I'm interested in finding a computationally efficient way for selecting all tuples of matrices which have a certain property. The property I'm interested in is that I want the column sum, of f[the ...
5
votes
2answers
125 views

Comparison Operation for Nested Matrices

I have a nested matrix n as bellow ...
2
votes
2answers
96 views

Creating function with matrix argument

I am completely new to programming, so I apologize in advance for a stupid question. I want to program an algorithm for computing invariant factors of a finitely generated abelian group, so in ...
2
votes
1answer
606 views

Rotation matrix $\to$ quaternion

I found a very good link about quaternions in Mathematica , but I don't know how to create a quaternion from a rotation matrix. Can anyone help me, please? Update I need this: A rotation may be ...
4
votes
6answers
523 views

Insert all elements from one matrix into another

I have two matrices $A$ and $B$ which are the same size. Each element of $A$ is a list of numbers. Each element of $B$ is just a number. How do I insert each element of $B$ into the corresponding list ...
0
votes
1answer
183 views

How to power-series expand determinants?

Say $g$ is a matrix which is given as, $g = g_0 + xg_2 + x^2 g_4 .. +x^{d/2 -1}g_{d-2}+ x^{d/2}(g_d + h_d(log (x)))$ where $d$ is an even number and each $g_i$ is a matrix (same dimension as $g$) and $...
0
votes
1answer
125 views

Matrix operations performed with column-vectors

We have 3 matrices: m1, m2 and b. We want to apply matrix operations (dot or sum) in a ...
2
votes
2answers
263 views

Measures of association, Concordant and Discordant

I want to calculate concordant and discordant pairs on nx2 tables. ...
4
votes
3answers
150 views

Creating nested matrix using random integers

How do i create 15x2 matrix with 2x2 random integer elements? My code only returned identical 2x2 elements:
33
votes
8answers
2k views

Longest path in 0/1 matrix

I have a matrix of 0's and 1's forming a number of disjoint paths:   I would like to find the lengths of the paths, and from that "spectrum," the longest length (in the above example: 27, ...
0
votes
1answer
167 views

Inverse of a restriction of a non-invertible matrix

Let $A∈R^{4×4}$ be a non-invertible matrix, with $2$-dimensional kernel. How can I compute the inverse of the restriction of $A$ on a subspace where it is invertible: $A^{-1}v \,\,\,\,$ where $\,\,\,\...
4
votes
1answer
587 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 ...
1
vote
2answers
242 views

Selecting parts of a matrix via indices given by a vector

I have a column vector of the form $\{1, 1, 2, 3, 2, 3\}^t$ and an associated matrix that has the same number of rows as the column vector, $6$, and a number of columns that is equal to the maximum of ...
3
votes
3answers
292 views

Algorithm to generate a certain matrix

I am looking for a convenient way to generate a matrix of the following symmetric form (numbers could also run from -3 to +3 or just from -1 to +1): Tips, anybody?
1
vote
1answer
148 views

Check every list element for appearance

I'm used to MATLAB so this might be a stupid question but Mathematica is freaking me out. I have a big matrix with the following format: ...