How to change matrix values in matlab without loop

Hi,

Assuming that I have the matrix A:

A =
  0.6638    0.9134    0.2785
  0.9058    0.3999    0.5469
  0.1270    0.0975    0.9168

I want to change the matrix value by the following condition without loops:

A(i,j) = (a)^2    if i=j and i=n+1-j
          2*a       otherwise

I read about sub2ind, It helped mw with the main diagonal but not the second diagonal (for i=n-j+1).

Any one can help me please?

Thanks in advance :)

[KSSV]

What is n? Does a stand for aij?

[Idan Cohen]

In my example n=3, but I need for n that stands for the matrix size

Answer 1

[Roger Stafford]

Assume A is n by n in size.

   A((1:n)+n*(0:n-1)) = a^2;
   A(n*(1:n)-(0:n-1)) = 2*a

Note: If n is odd, the two diagonals meet at the center. Depending on which rule is to have preference, you can do the above or reverse the order:

   A(n*(1:n)-(0:n-1)) = 2*a
   A((1:n)+n*(0:n-1)) = a^2;