how to multiply certain numbers in a matrice

if have a matrice A=[1,5,4;3,1,5;6,3,1] But I want to multiply only certain numbers for example A=[2,5,4;3,2,5;6,3,2] how do i do this.

Answer 1

[Guillaume]

You haven't explain what certain numbers mean. At a guess:

A(A == 1) = A(A == 1) * 2;

Answer 2

[Stephen23]

"certain numbers" == numbers along the diagonal ?

>> A = [1,5,4;3,1,5;6,3,1]
A =
   1   5   4
   3   1   5
   6   3   1
>> idx = 1==eye(3);
>> A(idx) = A(idx)*2
A =
   2   5   4
   3   2   5
   6   3   2