这两个矩阵为何不相等? [英] How come these two matrices are not equivalent?

问题描述

假设我们有一个3维数组F和2维矩阵S. 首先，我找到一个矩阵Y，该矩阵将F乘以S.然后，我尝试从Y中找到F的估计值(简称为F_est)，作为我代码中的健全性检查. 谁能看到逻辑上的缺陷，但我似乎不知道为什么F_est并不完全是F.

Assume we have a 3 dimensional array F and 2 dimensional matrix S. First I find a matrix Y which is F multiplied by S. Then I try to find an estimate of F (lets call it F_est) from Y as sanity check in my code. Can anyone see a flaw in logic, I dont seem to know why F_est is not exactly F.

F= randn(2,4,600);
S= randn(4,600);
for i =1:size(F,1);
    for j=1:size(F,2)
        for k= 1:size(F,3)
            Y(i,k)= F(i,j,k) * S(j,k);
        end
    end
end

for i =1:size(F,1)
    for j=1:size(F,2)
        for k= 1:size(F,3)
            F_est(i,j,k)= Y(i,k) / S(j,k);
        end
    end
end

然后我尝试查看F_est - F是否为零，否则为零.有任何想法吗.非常感谢.

then I try to see if F_est - F is zero and it is not. Any ideas. Much aprreciated.

****评论后编辑

基于我得到的答案，我想知道下面的代码是否有意义?

Based on the answers I got I am wondering if the code below makes any sense?

for k=1:size(F,3)
Y(:,k) = squeeze(F(:,:,k)* S(:,k)
end

如果我有Y和S，我可以恢复F吗?

Am I able to recover F if I have Y and S?

推荐答案

创建Y时，将连续替换其值.对于i,k对的任何值，您将覆盖Y j倍！

When you create Y, you are replacing its values continuously. For any value of pair of i,k you are overwriting Y jtimes!

这两个代码并不等效，因为F_est(i,j,k)仅计算一次，但是您有Y(i,k) j次.

Those 2 codes are not equivalent, as F_est(i,j,k) computed only once, but you have Y(i,k) j times.

我不知道您要做什么，但是未定义3D矩阵与2D矩阵的乘法，并且它不是2D矩阵

I don't know what you are trying to do, but a multiplication of a 3D matrix by a 2D matrix is not defined, and its not a 2D matrix

这篇关于这两个矩阵为何不相等?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！