I need to produce a matrix that has one's along the diagonal from the upper right to the lower left

I need to produce a matrix along a square matrix of size "n" that has one's along the diagonal from the upper right to the lower left. I can't use "for" or an "if" statement. Any idea?

What doesn't work is:

      function Y = reverse_diag(n)
      zeroes = zero(n);
      x = zero;
      x(1:1:n,n:-1:1) =1;
      Y = x;
      end

Answer 1

[DJ V]

Thanks, but use of diag is explicit;y forbidden.

[Walter Roberson]

Please click on "Comment on this Answer" instead of creating a new Answer.

Answer 2

[Walter Roberson]

 n:n-1:something

[Walter Roberson]

For example,

   Z = zeros(3,3);
   Z(3:2:7) = 1;

[Ahmet Cecen]

Oh yeah, you can also use linear indexing. Huh didn't even think of that.

[Walter Roberson]

Another hint:

Z = zeros(3,3);
Z(sub2ind([3 3], [1 2 3], [3 2 1])) = 1

Answer 3

[Ahmet Cecen]

x(1:1:n,n:-1:1) =1;

You cannot index points inside a matrix like that. MATLAB indexing reads like this:

Matrix(a,b) => For every a corresponding to every b.

So what you are doing is, say for the first row, fill every column (n:-1:1), then for the second row and so forth.

What you need to do is either use a for loop manually, or use the function:

diag()

followed by the function:

fliplr()