vectorization

2011 12 8
2 个回答
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1 个投票

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

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Dr. Seis
Dr. Seis 2011-12-8

1 个投票

If A is an NxN matrix:
A(1:N+1:N*N) = 0;

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Dr. Seis
Dr. Seis 2011-12-8
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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Sean de Wolski
Sean de Wolski 2011-12-8

1 个投票

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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