# Linked Questions

3answers
506 views

### generate a block matrix [duplicate]

We have two numbers: a and b, and $N$ submatrices (here $N=3$ but it should be generalized): ...
1answer
6k views

### Direct sum of matrices [duplicate]

Is there a simple way (perhaps even a built-in function) that allows one to compute the direct sum of two square matrices?
2answers
1k views

### Create a matrix of matrices using Band and ArrayFlatten [duplicate]

I can easily write a simple Band matrix using: SparseArray[{Band[{2, 1}] -> a}, {Dim, Dim}] where a is a number. Now, I ...
4answers
946 views

### Prepend 0 to sublists

My question is similar to this one, but my goal is to prepend a single 0 the each sublist, not incrementally many 0's. The file I'm working is a CSV containing around 50K sublists of length 35. I've ...
3answers
1k views

### Speeding up generation of block diagonal matrix

I'm struggling with the following problem. I have $48$ square matrices (full, filled with real machine precision numbers, thus are packed, all different) of size $128$. I wolud like to place them on a ...
5answers
423 views

### How to form a diagonal matrix from sub-matrices?

I have a 3x3 matrix (let's say G) and a 3x3 matrix of zeros (let's say zero). I want a diagonal matrix in the form Diag[G; G; G; zero] such that the size of matrix becomes 12x12. I actually have to ...
3answers
1k views

### How to build a matrix from a set of vectors and other matrices using ArrayFlatten

I want to build a 6 by 3 matrix, from the following: one vector is 3 by 1, then a matrix, which is 3 by 2. These will go to the top 3 rows. Now the bottom 3 rows, I'll have 3 vectors each is 3 by 1. ...
4answers
1k views

### How to extract the list of all matrices from a Block Diagonal Matrix?

I am working on a function to do the opposite operation of How to form a block-diagonal Matrix from a list of matrices? Here is my current algorithm: For i ...
3answers
554 views

### Joining matrices together

Given the following matrices (where $n$ can be any integer number, It is just for a general dimension of my space): ...
3answers
982 views

### How to create a block diagonal matrix by repeating a submatrix $n$ times?

If there is a submatrix, let's call $P$: $P=\begin{pmatrix} 1 & 1 \\ 1 & 1 \end{pmatrix}$ And I want to have $n$, let's say $n=2$, such submatrices placed on the diagonal. The result is ...
3answers
1k views

### How to create a large sparse block matrix

I need to generate a very large sparse block matrix, with blocks consisting only of ones along the diagonal. I have tried several ways of doing this, but I seem to always run out of memory. The ...
1answer
1k views

### Add a sub-matrix of zeros in big matrix [duplicate]

I have a matrix of size $24\times24$ composed by 8 $3\times3$ submatrices in a diagonal way. I want to add a matrices of zeros ($3\times3$) between the sub-matrices, so the final matrix would be of ...
1answer
795 views

### Building a matrix in block matrix format

Now, I'm aware of the threads existing about this question such as: How to enter matrices in block matrix format? How to form a block-diagonal Matrix from a list of matrices? But I wasn't able to ...
2answers
51 views

### Concatenate matrices in a specific way

Is there an elegant way to start with a matrix of the form $$A = (B,C)$$ where B and C have dimensions n x m, and construct a large matrix that looks like  \begin{pmatrix} B & C & \mathbf{...