How to operate on specific diagonal elements of a matrix?

Hello everyone.

I am having a matrix k with size (20 x 20), for which, I need to replace some of the diagonal elements with ones. I constructed a vector v including the indices of the elements to be replaced, and applied the following code, but I is not working as I wanted.

k = rand(20);
u = [1; 3; 6; 11; 16; 20];
k(u(:,1),u(:,1)) = 1;

He is replacing the diagonal members and other members as if he is including all combinations of the rows and columns. How can I edit this to get only the diagonal members corrected?

Answer 1

[Stephen23]

You need to use sub2ind:

>> idx = sub2ind(size(k),u,u);
>> k(idx) = 1

[Ahmad Gad]

Thank you so much, it worked fine.