I have a huge matrix to A to solve for Ax=B. There are some rows with zero elements in A and I want to modify the diagonal for these rows. So how can I fast find these rows with all zero elements? for loop is rather slow.

I have a huge matrix to A to solve for Ax=B. There are some rows with zero elements in A and I want to modify the diagonal for these rows. So how can I fast find these rows with all zero elements? for loop is rather slow.

Answer 1

[KSSV]

A = [0 0 0 ; 1 2 3; 4 5 6] ;
idx = sum(A,2)==0
A(idx,:)

Or Simply:

A = [0 0 0 ; 1 2 3; 4 5 6] ;
idx = any(A,2)
A(idx,:)

[yangyang qiao]

Thanks, How to set diagonal as 1 for the row with all zero elements?

[KSSV]

If you got rth row....

A(1,r) = 1 ;

Answer 2

[Andrei Bobrov]

"How to set diagonal as 1 for the row with all zero elements?"

A = A + diag(~diag(A));

or

n = all(A==0,2);
A = A + diag(n);

or

n = all(A==0,2);
ex = (1:size(A,1)+1:numel(A))';
A(ex) = A(ex) + n;

[yangyang qiao]

thanks, your code can change the diag when diag is 0, what I hope is that change the diag when the whole row is 0