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How to improve a for

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Carlos
Carlos 2014-10-11
编辑： Andrei Bobrov 2014-10-11
Hello, i want to do this operation:
f = -[Q(:,1)'*Q(:,1); Q(:,2)'*Q(:,2); Q(:,3)'*Q(:,3); Q(:,4)'*Q(:,4); Q(:,5)'*Q(:,5); Q(:,6)'*Q(:,6); Q(:,7)'*Q(:,7); Q(:,8)'*Q(:,8); Q(:,9)'*Q(:,9); Q(:,10)'*Q(:,10)];
i have thought to do this with a for
n=10;
i=1;
while i<n+1
f(i,1)=-[Q(:,i)'*Q(:,i)]; %save in columns
i=i+1;
end
but i think there must be some way to vectorize this easily. Could you help me?
Thank you.

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2014-10-11
-sum(Q.*Q)

更多回答（2 个）

Jan
Jan 2014-10-11
The vectorization is better, but here is a cleaner and more efficient loop method:
f = zeros(10, 1); % pre-allocate!!!
for k = 1:10
f(k, 1) = -(Q(:,k)' * Q(:,k));
end
  2 个评论
Carlos
Carlos 2014-10-11
Thank you so much. I think that the for loop is much better than mine before. Otherwise, how is the way to make the vectorization? Is it the answer of Azzi?
Jan
Jan 2014-10-11
Yes, Carlos.

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Andrei Bobrov
Andrei Bobrov 2014-10-11
编辑：Andrei Bobrov 2014-10-11
f = -dot(Q,Q).'

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