Multi Dimension Matrix Elements multiplication

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sko
sko el 24 de Feb. de 2021
Respondida: Steven Lord el 24 de Feb. de 2021
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)?
Thanks in advance

Respuestas (2)

Rik
Rik el 24 de Feb. de 2021
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

Steven Lord
Steven Lord el 24 de Feb. de 2021
If you're using release R2020b or later, see the pagemtimes function.

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