speed up for loop

Question

Sana Tayyeb 2015-3-21

1
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https://ww2.mathworks.cn/matlabcentral/answers/184376-speed-up-for-loop

编辑： Stephen23 2015-3-26

My code comprises of for loop which has up to 100 and sometimes 1000 increments and processing takes a long time. Is there a way to speed up this code? Please guide me

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Sana Tayyeb 2015-3-22

call_perl.m

yes i meant iterations. Sorry for my mistake. see my code it reads from a file and download files using perl script and saves those files in an other file.

Image Analyst 2015-3-22

And did you use profiler like Stephen suggested or click the "Run and time" button? If not, why not?

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Answer 1

Stephen23 2015-3-21

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https://ww2.mathworks.cn/matlabcentral/answers/184376-speed-up-for-loop#answer_172217

编辑：Stephen23 2015-3-21

Although you have not given any details at all of your code, there are several ways you can speed up your code:

use vectorized code rather than loops.
preallocate arrays before loops.
use logical indexing rather than subscripts.
do not change a variable's data class.
use tic and toc to time parts of a program.
use the profiler to check how long all parts of a function require.

In the MATLAB documentation we also find these tips:

Additional Tips on Improving Performance

If the performance of your program remains a concern, then consider the following suggestions:

Split large script files into smaller ones, having the first file call the second if necessary.
Construct separate functions (or local functions and nested functions) from the larger chunks of code.
If you have overly complicated functions or expressions, use simpler ones to reduce size. * Simpler functions often make good utility functions that you can share with others.
Use functions instead of scripts because they are generally faster.
Vectorize your code to take advantage of the full functionality of MATLAB.
Use a sparse matrix structure to vectorize code without requiring large amounts of memory.
Avoid running large processes in the background while executing your program in MATLAB.
Avoid overloading MATLAB built-in functions on any standard MATLAB data classes because this can negatively affect performance.