将矩阵的每一列乘以另一个矩阵 [英] Multiply each column of a matrix by another matrix

问题描述

我有一个M x N矩阵.我想将每个N列乘以M x M矩阵.以下是循环执行的操作，但是我不知道如何对其进行矢量化处理.

I have a M x N matrix. I want to multiply each of the N columns by a M x M matrix. The following does this in a loop, but I have no idea how to vectorize it.

 u=repmat(sin(2*pi*f*t),[n 1]);
 W = rand(n);
 answer = size(u);
 for i=1:size(u,2)
   answer(:,i) = W*u(:,i);
 end

推荐答案

您只需要将两个矩阵相乘即可​​.

You simply need to multiply the two matrices:

answer = W*u;

考虑一下:在循环的每次迭代中，都将矩阵乘以向量.该操作的结果是一个向量，您可以将其保存到第i列的答案中.矩阵乘法是类似的事情:您可以将其理解为矩阵(W)与一组向量的乘法，这些向量构成了矩阵u.

Think about it: in every iteration of your loop you multiply a matrix by a vector. The result of that operation is a vector, which you save into your answer in column i. Matrix multiplication is a similar thing: you can understand it as multiplication of a matrix (W) by a set of vectors, which form your matrix u.

所以您的代码很好，只需删除循环即可:)

So your code is good, just remove the loop :)

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