logical indexing shortcut?

[Peter P.]

Hi list,

I am looking for a way to operate on certain elements of a vector using
logical indexing. I want to multiply all elements in x that are integer
multiples of four by the number 5.

x = [3 15 9 12 -1 0 -12 9 6 1];
b = rem(x, 4)==0;
x(b) = x(b)*5

I wonder if there is a way to do it in one step, without creating index
vector b? I know it works when assigning static values as in

x(rem(x, 4)==0) = -1

Any help is very welcome!
P