Matlab to extract the n th diagonals in a Matrix

I have a matrix, for example A=[ 1 0 0 0 ; 0 2 0 0 ; 0 0 3 0 ; 0 0 0 4]; I want to reference to the n th diagonal, for example the 2nd and 4th ones, that means [2,4]. Is there a elegant way to do this without using a loop. I tried using A([2,4],[2,4]) but it gave a 2*2 matrix. Anybody knows how to do this? Thanks.

Answer 1

[Thorsten]

d = [2 4]; A(sub2ind(size(A), d, d))

[Xin]

Thank you Thorsten. That does solve the problem. :)

Answer 2

[michio]

Have you considered using diag function?

 A=[ 1 0 0 0 ; 0 2 0 0 ; 0 0 3 0 ; 0 0 0 4];
 dA = diag(A); 
 dA([2,4])
  ans =
       2
       4

[Xin]

Thanks a lot for your answer Michio. I actually wanted to index the 2nd and 4th components. This will give me the number but I actually need to change the value of the 2nd and 4th components.

Answer 3

[Andrei Bobrov]

A = randi(9,5);
n = [2,4];

A(sub2ind(size(A),n,n)) = 100*n;

[Xin]

Thanks. That works.