pointwise multiplication with ndSparse arrays slower than using full arrays

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Sandra Martinez 2022-12-13

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https://ww2.mathworks.cn/matlabcentral/answers/1877292-pointwise-multiplication-with-ndsparse-arrays-slower-than-using-full-arrays

关闭： Matt J 2022-12-14

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Hi Matt. I measure the times making pontiwise multiplication with full arrays vs ndSparse arrays and the first one tooks less time (a factor 7).

n=50;
for i=1:20;
    M=rand(n,n,n,n);
    N=zeros(n,n);
    N(1,1)=2;
    tic
    L=M.*N;%pointwise multiplication with full arrays
    t1=toc;
    tt(i)=t1;
    A=ndSparse(M);%You need to download this function
    B=sparse(N);
    tic
    C=A.*B;%pointwise multiplication using sparse arrays
    
    t2=toc;
    tt2(i)=t2;
end
%%
% mean(tt)
%    0.0045
%mean(tt2)
% 0.0350

But if both are matices the time is the other way arround

for i=1:20;
    M1=rand(n,n);
    N1=zeros(n,n);
    N(1,1)=2;
    tic
    L1=M1.*N1;
    t3=toc;
    tt3(i)=t3;
    A1=ndSparse(M1);
    B1=sparse(N1);
    tic
    C1=A1.*B1;
    t4=toc;
    tt4(i)=t4;
end
mean(tt4)/mean(tt3)
% 5.8859 doing pointwise multiplication using sparse matrices it is almost 6
% times faster.