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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)')
``````

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

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