Question

In my code, I have to multiply a matrix A (dimensions 3×3) to a vector b1 (dimensions 3×1), resulting in C. So C = A*b1. Now, I need to repeat this process n times keeping A fixed and updating b to a different (3×1) vector each time. This can be done using loops but I want to avoid it to save computational cost. Instead I want to do it as matrix and vector product. Any ideas?

Answer 1

You need to build a matrix of b vectors, eg for n equal to 4:

bMat = [b1 b2 b3 b4];

Then:

C = A * bMat;

provides the solution of size 3×4 in this case. If you want the solution in the form of a vector of length 3n by 1, then do:

C = C(:);

Can we construct bMat for arbitrary n without a loop? That depends on what the form of all your b vectors is. If you let me know in a comment, I can update the answer.