Vectorize a double loop
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Hi everyone
I'm tryng to vectorize the folowing piece of code:
n=30;
d=3;
a=1;
b=2;
cell=3;
for ki = 2:n-1
for kj = 2:n-1
M((cell-1)*n^2+(ki-1)*n+kj,(cell-1)*n^2+(ki-1)*n+kj-1) = 1/d^2;
M((cell-1)*n^2+(ki-1)*n+kj,(cell-1)*n^2+(ki-1)*n+kj) = -4/d^2-a;
M((cell-1)*n^2+(ki-1)*n+kj,(cell-1)*n^2+(ki-1)*n+kj+1) = 1/d^2;
M((cell-1)*n^2+(ki-1)*n+kj,(cell-1)*n^2+(ki-1)*n+kj-n) = 1/d^2;
M((cell-1)*n^2+(ki-1)*n+kj,(cell-1)*n^2+(ki-1)*n+kj+n) = 1/d^2;
C((cell-1)*n^2+(ki-1)*n+kj,1) = b;
end
end
How can I do it? I will appreciate any help! Thanks!
3 个评论
Walter Roberson
2021-5-10
What are we to presume about the datatype and size of cell ? It does not appear to be a cell array.
Walter Roberson
2021-5-10
(cell-1)*n^2+(ki-1)*n+kj
You are faking 4 dimensional indexing. You should switch to actual 4D indexing. reshape() before and after if you need to.
Walter Roberson
2021-5-13
If you feel that your post is unclear, then since you are the one who wrote it, you should clarify it.
回答（1 个）
Bob Thompson
2021-5-10
Does this work? I haven't been able to test it.
M((cell-1)*n^2+(1:n-2)*n+(2:n-1),(cell-1)*n^2+(1:n-2)*n+(2:n-1)-1) = 1/d^2;
M((cell-1)*n^2+(1:n-2)*n+(2:n-1),(cell-1)*n^2+(1:n-2)*n+(2:n-1)) = -4/d^2-a;
M((cell-1)*n^2+(1:n-2)*n+(2:n-1),(cell-1)*n^2+(1:n-2)*n+(2:n-1)+1) = 1/d^2;
M((cell-1)*n^2+(1:n-2)*n+(2:n-1),(cell-1)*n^2+(1:n-2)*n+(2:n-1)-n) = 1/d^2;
M((cell-1)*n^2+(1:n-2)*n+(2:n-1)j,(cell-1)*n^2+(1:n-2)*n+(2:n-1)+n) = 1/d^2;
C((cell-1)*n^2+(1:n-2)*n+(2:n-1),1) = b;
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2021-5-13
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