function y = scale_rows(x,s)
% SCALE_ROWS      Scale each row of a matrix.
% SCALE_ROWS(x,s) returns matrix y, same size as x, such that
% y(i,:) = s(i)*x(i,:)
% It is more efficient than diag(s)*x.

y = repmat(s(:), 1, cols(x)).*x;
%y = (s(:)*ones(1,cols(x))).*x;