How to optimize a matrix multiplication in MATLAB?

Question

Can I somehow optimize this formula? I evaluate it many times and it takes much time...

w - 1xN double

phis - NxN double

x - Nx2 double

sum(w(ones([size(x, 1) 1]),:).* phis, 2)

Answer 1

You're taking the scalar product of each row of phis with w . You can do this easily using linear algebra.

out = phis * w';

This matrix multiplication saves you calls to sum , ones , and size , which should make your code a lot faster. Furthermore, linear algebra operations are often very fast in Matlab, since that's what the program is historically optimized for.