MATLAB Answers

Zhi
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Why the external dos command/program is so slow in 64 bit window?

Asked by Zhi
on 22 Feb 2011
Latest activity Edited by Jan
on 3 May 2017
Hi,
I try executing some external commands/programs in Matlab (R2010a, 64bit) but they are very slow. Here is an example: Matlab program: disp('Test external command in Matlab');
for i = 1:5 tic system('cd .'); toc end
Results: Test external command in Matlab Elapsed time is 7.136996 seconds. Elapsed time is 6.094630 seconds. Elapsed time is 5.574957 seconds. Elapsed time is 6.235473 seconds. Elapsed time is 5.973438 seconds.
My computer is Dell Optiplex 980, Windows 7. I have not met the same problem in Linux or 32bit Matlab.

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4 Answers

Answer by Jan
on 22 Feb 2011
Edited by Jan
on 3 May 2017

This can depend on "cd .". If the current directory contains 7000 files and is on a network drive connected by a 100MBit ethernet, 6 seconds are not really surprising.

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Answer by the cyclist
on 22 Feb 2011

I am using R2010b on a 64-bit Mac, and I do not see that behavior. My elapsed times are on the order of milliseconds.

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Answer by Aviv Rosenberg on 31 Oct 2016
Edited by Walter Roberson
on 31 Oct 2016

Try this:
Haven't tested on windows, but it really speeds up my workflow on OSX.

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I notice that the source does
pb.redirectErrorStream(true);
I am wondering if that affects explicit I/O redirection the user may have given on the command line, such as if the command were
someCommand SomeArguments 2>SomeOutputFile
because the user wanted stderr to go to a file?

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Answer by Xiangrui Li on 3 May 2017

I observed the slowness for both win32 and win64. I just posted a question why redirecting the output to a file improve the performance. It is strange that, even if there is no output, redirecting still makes it faster.
tic, for i = 1:5, system('cd .'); end; toc
Elapsed time is 0.627796 seconds.
tic, for i = 1:5, system('cd . >myFile'); end; toc
Elapsed time is 0.111956 seconds.

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