How to copy a sub-matrix/vector along diagonal of a larger matrix with varying number of sub-matrices?

I want to create a matrix below where I copy A = [1 2 3] allow the diagonal of a matrix.

[ 1 2 3 0 0 0 0 0 0 0 0 0

0 0 1 2 3 0 0 0 0 0 0

0 0 0 0 0 0 1 2 3 0 0 0

0 0 0 0 0 0 0 0 0 1 2 3]

I know I can use blkdiag(A ,A, A, A) which will do the job however the number of parameters vary in my code. Sometimes, there may be five A vectors or 20 A vectors that I need to create such a matrix. Let's say this is a variable that the user inputs

How can I do this efficiently in code?

[Sean de Wolski]

I'm not clear, how would result be different with five vectors or twenty?

[John]

If I wanted 5 vectors, it would be blkdiag(A, A, A, A, A) If I wanted 20 vectors, it would be blkdiag(A, A, A, A....A, A, A)

I don't know how many A vectors I need so the input to blkdiag would change each time.

Answer 1

[Sean de Wolski]

You can use comma-separated list expansion to do this automagically:

n = 20;
A = [1 2 3];
Ac = repmat({A},n,1);
blkdiag(Ac{:})

Answer 2

[Azzi Abdelmalek]

a=[1 2 3]
n=5
d=[a zeros(1,numel(a)*(n-1))]
out=cell2mat(arrayfun(@(x) circshift(d,[0 (n-1)*x]),(0:n-1)','un',0))

EDIT

a=[1 2 3]
n=5
d=[a zeros(1,numel(a)*(n-1))]
out=cell2mat(arrayfun(@(x) circshift(d,[0 numel(a)*x]),(0:n-1)','un',0))

[Azzi Abdelmalek]

There was an error, check this

n=5     % number of matrices
a=[1 2 3]
d=[a zeros(1,numel(a)*(n-1))]
out=cell2mat(arrayfun(@(x) circshift(d,[0 numel(a)*x]),(0:n-1)','un',0))

Answer 3

[Azzi Abdelmalek]

n=10
a=[1 2 3]
s= ['@(x1)blkdiag(x1' sprintf(',x%d',ones(1,n-1)) ')']
blkdiagn=str2func(s)
out=blkdiagn(a)

Answer 4

[George Papazafeiropoulos]

e = ones(n,1);

A = full(spdiags([e 2*e 3*e], 0:2, n, n+2))

A = full(spdiags(A, 0:5, n, n+5))

A = full(spdiags(A, 0:8, n, n+8))

George Papazafeiropoulos