I get different results for the product of two matrices?

Question

mehra 2022-11-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1846828-i-get-different-results-for-the-product-of-two-matrices

移动：Matt J 2022-11-9

采纳的回答： Marcel Kreuzberg

u.mat
w.mat

在 MATLAB Online 中打开

Hello

For my u.mat and w.mat data sets I need to do a calculation to find:

u-mean(u) and w-mean(w) and then find the mean of their products.

but when I define this calculation in one line (as in results(2,np)) it gives different results from when I define u_differ and w_differ separately, and then find the mean of their product (results(1,np)). Since I will have some other calculations I prefer to make it short. So I would like to know what is wrong with results(2,np) line that gives different results from results(1,np) although they're the same definition in fact

load('u.mat')
load('w.mat')
results=zeros(2,2);
for np=1:2;
    u_differ(:,np)=u(:,np)-mean(u(:,np));
    w_differ(:,np)=w(:,np)-mean(w(:,np));
    results(1,np)=mean(u_differ(:,np).*w_differ(:,np));
    results(2,np)=mean(u(:,np)-mean(u(:,np)).*w(:,np)-mean(w(:,np)));   
end