Diagonal of a non-squared martrix

Hello all,

I have a matrix A=zeros(179,716)

and I am trying to put the value "1" in its diagonal

however it's not a squared matrix so I don;t know how to this!

any ideas?

thanks a lot

Answer 1

[Nikolas Spiliopoulos]

Alright thanks a lot!!!!

Answer 2

[Wick]

MATLAB has a built-in function for the identity matrix, 'eye'. There are two diagonals in a non-square matrix. We'll set both, one at a time. If you only want the first, don't use the second line.

A=zeros(179,716);
E = eye(179);

% Here's where we set the first diagonal
A(:,1:179) = E;

% we don't want to stop on the 1's already there 
% so we use a max to keep the larger value
A(:,(end-179+1):end) = max(E, A(:,(end-179+1):end) ); 

% Your matrix is actually wide enough the second definition 
% doesn't need the max, but if it was closer to a square you 
% wouldn't want to stomp on the ones already there. Instead of 
% a max command you could also add the subset of A to the identity
% matrix.

[Nikolas Spiliopoulos]

thanks a lot!!

[Nikolas Spiliopoulos]

Thanks for the answer! However I realized that it doesn't put 1 for the columns : 180-537

[Wick]

But that's not a diagonal. Diagonals start in corners. If you want the diagonal to repeat 4 times across the array you could use 'repmat' to make a 1,4 array of the identity matrix and overwrite the original. Actually, since all you want is the zeros and ones, you can start right there:

A = repmat(eye(179),1,4);

Edit, I suppose any diagonal is a diagonal. But I thought you meant the major diagonals. In a square that would be from top left to bottom right. In a rectangular array it would be top-left to bottom and bottom-right to the top.