How expand a matrix?

How we can expand matrix A to B? each element of matrix A is equal to sum of each B columns. (step of 3)

A=

[1 5 8 12 7 5 2 1]

to B=

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

[jgg]

Aren't there a very large number of ways to do this? Is there some specific form you want?

[Star Strider]

It seems that it’s constrained to use only {1, 2, 3}. That may be what ‘step of 3’ refers to.

[Mori]

I will use this code for a large Matrix with large numbers. 3 is the gris size, in real data will be 300. I will post the results. Thanks

[Mori]

Yea, works perfectly. Thnaks

Answer 1

[jgg]

This should work

 A = [1 5 8 12 7 5 2 1];
 floors = floor(A./3);
 C = cumsum(3.*ones(max(floors)+1,length(A)),1)
 A_p = repmat(A,max(floors)+1,1);
 res = 3.*(C <= A_p);
 remainder = A - sum(res);
 r = cellfun(@(row) find(row == 0, 1, 'first'), num2cell(res,1));
 ind = sub2ind(size(res),r,[1:length(A)]);
 res(ind) = remainder;

[Mori]

thanks, it works