Problem 1321. Given a 4x4 matrix, swap the two middle columns

If

 a = [1 2 3 4; 1 2 3 4; 1 2 3 4; 1 2 3 4];

then the result is

 ans =

     1     3     2     4
     1     3     2     4
     1     3     2     4
     1     3     2     4

Perform a simple swap of the two middle columns.