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@jellied_unagi

mat2cell vs forループ

More than 5 years have passed since last update.

mat2cell駆使してたらえらい遅いことに気がついたので,簡単な実験をしてみた.
ランダムな正数の入ったN*1の行列をN*1 個のcellに分割する(N=1e1,1e2,...,1e7).
ご指摘等ありましたらよろしくお願いします.

mat2cell-vs-for.m
t1=zeros(7,1);
t2=t1;
for n=1:7
    N=10^n;
    a=randi(N,N,1);
    % mat2cell
    tic
        out=cell(N,1);
        out=mat2cell(a,ones(N,1));
    t1(n)=toc
    %
    % for
    tic
        out=cell(N,1);
        for i=1:P
            out{i}=a(i);
        end
    t2(n)=toc
end
% visualization
plot(1:7,[t1,t2])
legend({'mat2cell','for-loop'})
set(gca,'XTickLabel',{'1e1','1e2','1e3','1e4','1e5','1e6','1e7'})
xlabel('Vector size')
ylabel('Elapsed time (sec)')

実験結果
Mac Pro (Mid 2010)
OS: 10.7
processor: 2 x 2.66GHz 6-Core Intel Xeon
mem: 16GB
Matlab 2012a

t1 =
0.0008
0.0006
0.0047
0.0437
0.4256
4.2257
43.2572

t2 =
0.0003
0.0000
0.0002
0.0014
0.0187
0.1723
1.4863

結果

コード的にはmat2cellのが断然きれいなのだけど,データのサイズが大きくなると計算時間は比較にならないようです.分割数を変えた場合や,分割サイズを可変にした場合どうなるかについては,未検証…

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jellied_unagi
Python and Matlab tips for computer vision

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Help us understand the problem. What is going on with this article?