How to improve a for

1 次查看（过去 30 天）
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.

请先登录，再回答此问题。

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.

请先登录，再进行评论。

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

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

产品

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by