Question

Suppose I have Matrix A:

A =

 1     2     3
 4     5     6   

For every element x<2, add 10,
for every element x>5, add 20, and
for every element 2<=x<=5, add 30.

So for my example matrix A, I need to end up with the following matrix B:

B = 

11    32    33
34    35    26

I need to be able to do this in a general way, since the actual matrix will be quite large. Any suggestions? Can I use the IF statement?

Answer 1

You don’t need an IF you need logical indexing:

    IndexOfLessThan2 = A < 2;
    IndexOfGreaterThan5 = A > 5;
    IndexBtw2and5 = ~(IndexOfLessThan2 | IndexOfGreaterThan5);

    A = A + IndexOfLessThan2*10 + IndexOfGreaterThan5*20 + IndexBtw2and5*30;