Say I am given a row vector psi of length P and a row vector q of length M in MATLAB. Here, M>P. I want to assemble G in the following way:

for j = 1:M
        G(j) = q(j:min(j+P-1, M))*psi(1:min(M-j+1, P))';
end

For large M, P, this is very time consuming. It is also delicate to the size of qand psi changing for large j.

I have not been able to vectorize this, also due to j moving. Of course, one could write this as a matrix-vector multiplication with psi being the vector, but assembling the correct matrix looks almost equally expensive to me.

I appreciate any sort of help.