Questions on the manipulation of matrices in Mathematica.

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16
votes
4answers
2k views

What is the right way to rotate an array?

Suppose I have an array, not necessarily square: a = $\left( \begin{array}{ccc} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{array} \right)$ I want to rotate it like one ...
17
votes
3answers
416 views

How to improve this code for exploring large matrices?

What I'm actually trying to do is to elaborate this question. I'd like to use Pane with scrollbars enabled to explore large (sparse) matrices like this one: Here ...
10
votes
1answer
1k views

Nesting Parallel processes

I just attempted to run code that had nested ParallelMap[] functions. It generates the error message: ParallelMap::subpar: Parallel computations cannot be nested; proceeding with sequential ...
10
votes
1answer
1k views

How to apply a permutation to a symmetric square matrix?

Given a symmetric square matrix, how can I apply a permutation to the rows and columns (i.e. the same permutation to both the rows and the columns) such a way that the new structure of the matrix ...
5
votes
1answer
3k views

Simpler way of performing Gaussian Elimination?

Is there a simpler way of performing Gaussian Elimination other than using RowReduce? Such as a single built in function? Edit: Look at the example from our simulation class. Not too difficult, but ...
15
votes
4answers
1k views

What is the fastest way to locate an image inside a larger image?

let b = let c = How to do: find[c,b] that returns the bounding box of c in b? ...
3
votes
1answer
402 views

Take[] and other Mathematica functions with live streams

I have a live video feed that I would like to convert into raw numbers that could be used for a variety of different things. I would also like to do simple operations on these numbers live with as ...
24
votes
2answers
5k views

How to enter matrices in block matrix format?

Example: I have a matrix $R = \left( \begin{array}{cc} A & \mathbf{t} \\ 0 & 1 \end{array} \right) $ where $A$ is 3-by-3 and $\mathbf{t}$ is 3 by 1. Or in Mathematica ...
9
votes
3answers
2k views

Why don't * and ^ work as I expected on matrices?

For example, this input... {{1, 2}, {3, 4}}*{{1, 2}, {3, 4}} produces this output... {{1, 4}, {9, 16}} and this input... ...
33
votes
5answers
8k views

What is the most efficient way to add rows and columns to a matrix?

Say I have a matrix m and a vector v. ...
70
votes
2answers
3k views

Flatten command: matrix as second argument

One thing I could never wrap my head around is how Flatten works when provided with a matrix as the second argument, and the Mathematica help isn't particularly ...
24
votes
3answers
3k views

How to symbolically do matrix “Block Inversion”?

Consider a block (partitioned) matrix matrix = ArrayFlatten[{{a, b}, {c, d}}] where, a, ...