Access to array elements

Hi,

I have a matrix, A, and I want to access the elements given by the vectors ind_rows, ind_cols. If I make A(ind_rows,ind_cols) I get a matrix of size ind_rows times ind_cols, but I am just interested in the diagonal of this matrix!

I have found a way to do this:

siz = size(A);
AA  = A(1:end); % convert the matrix in a vector
IND = sub2ind(siz,ind_rows,ind_cols);
res = AA(IND);

It works, but I guess there must be a way to do this without rearranging the matrix in a vector, and in a cleaner way.

Thanks in advance!

Ana

Answer 1

[Pavl M.]

http://www.mathworks.com/help/techdoc/math/f1-85462.html

Kindest Regards.

my web resource: http://goo.gl/2gh7X

[Ana]

So I guess it would be enough with:

siz = size(A);

IND = sub2ind(siz,ind_rows,ind_cols);

res = A(IND);

Thank you!

Answer 2

[Image Analyst]

Ana: The most common way to get the diagonals is to use the eye() function:

m_DiagonalsOnly = m(logical(eye(size(m, 1))))

[Ana]

The problem is that in some cases the matrix A(ind_rows,ind_cols) is too big to be generated, so I needed something that did not create that matrix.

Anyway I am not sure I am understanding properly your suggestion, since to get the diagonal of a matrix I can just simply the diag command, can't I?

Thank you.