Simple Question about Optimization of a FOR loop

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Mohsen
Mohsen 2013-6-14
How can I optimize (vectorize?) the following code in order to avoid the for loop and make the code to run faster?
for i=1:55;
A(i)=B((i-1)*3+1,1);
end
A is 1 x 55 and B is 165 x 1
Many thanks!

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回答（2 个）

Laila Kazemi
Laila Kazemi 2013-6-14
C= B*3 +1 A (1:55, 1:55)= C(1:55, 1)
but the dimensions of ur matrices dont match , if B was 55 by 1 , it would have worked
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Laila Kazemi
Laila Kazemi 2013-6-14
actaully instead one make a matrix called D with D( , 1:165)=(1)
Mohsen
Mohsen 2013-6-16
Thanks for your answer but it doesn't seem to be the right answer... Please note that the multiplication by 3 and the addition by 1 is used to access the content of each element and not to modify the content of the elements...
I found this answer and it worked:
A=B(1:3:55*3,1);
Thanks again.

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Andrei Bobrov
Andrei Bobrov 2013-6-14
A(1,:) = B((0:size(A,2)-1)*3+1);
  1 个评论
Mohsen
Mohsen 2013-6-16
Thanks for your answer but it doesn't seem to be the right answer...
I found this answer and it worked:
A=B(1:3:55*3,1);
Thanks again.

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