# Multi Dimension Matrix Elements multiplication

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sko 2021 年 2 月 24 日

Hello,
I am strugling with some matrix multiplication...
I am having one M: matrix and one N: matrix with some given elements. Elements of M are given as whereas elements of N are given as . I wish to obtain maxtrix P: whose elements , and . Thus, matrix would be in my case.
Does anyone know how to perform this complex operation in the fastest way (without loops)?

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### 回答 (2 件)

Rik 2021 年 2 月 24 日
Not completely without loops, but this should be fast enough. You should also be aware that loops can sometimes be the fastest way.
M=rand(3,2);N=rand(2,3,4);
%prime the execution engine to produce a more reliable comparison
timeit(@()option1(M,N));
timeit(@()option1(M,N))
ans = 1.5263e-05
timeit(@()option2(M,N))
ans = 5.3950e-06
isequal(option1(M,N),option2(M,N))
ans = logical
1
function P=option1(M,N)
P=zeros(size(M,1),size(N,2),size(N,3));
for n=1:size(M,1)
P(n,:,:)=M(n,1)*N(1,:,:)+M(n,2)*N(2,:,:);
end
end
function P=option2(M,N)
P=zeros(size(M,1),size(N,2),size(N,3));
for i=1:size(M,1)
for j=1:size(N,2)
for k=1:size(N,3)
P(i,j,k)=M(i,1)*N(1,j,k)+M(i,2)*N(2,j,k);
end
end
end
end
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Steven Lord 2021 年 2 月 24 日
If you're using release R2020b or later, see the pagemtimes function.

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