# vectorization

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Steven on 8 Dec 2011
hi,
is there a quick way to change the values of the diagonal of a matrix, instead of
for i = 1:length(A)
A(i,i) = 0;
end
thx
##### 1 CommentShowHide None
Andrei Bobrov on 8 Dec 2011
A-diag(diag(A))

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### Accepted Answer

Dr. Seis on 8 Dec 2011
If A is an NxN matrix:
A(1:N+1:N*N) = 0;
##### 1 CommentShowHide None
Dr. Seis on 8 Dec 2011
N = 10000;
A = rand(N);
tic
A(1:N+1:N*N)=0;
toc % Took 0.000532 seconds
A = rand(N);
tic
A(logical(speye(length(A)))) = 0;
toc % Took 0.001379 seconds
A = rand(N);
tic
A = A - diag(diag(A));
toc % Took 0.215796 seconds

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### More Answers (1)

Sean de Wolski on 8 Dec 2011
One way:
A = magic(100); %sample matrix
A(logical(speye(length(A)))) = 0;
Also diag if you're building a matrix
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