speed up for loop

2015 3 21
1 个回答
更新时间：2015 3 26
13 次查看（30 天）

1 个投票

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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Chad Greene
Chad Greene 2015-3-21
A good answer will require details. Give the simplest possible example of your code and maybe we can help.
Image Analyst
Image Analyst 2015-3-21
Perhaps you mean iterations rather than increments. But that's a very small loop - it should take as short as a new nanoseconds, depending on what you're doing inside it. Of course, if there is a pause(5) inside the loop, it could take 5 seconds per iteration. What's inside your loop?
Stephen23
Stephen23 2015-3-21
编辑：Stephen23 2015-3-26
@Sana Tayyeb: You don't give us any information at all about what code you are using, so how are we supposed to help you improve it? Sorry but we can't read your mind or your computer screen, so you actually need to give us some useful details about what you are using. Best of all you could upload your complete code using the paperclip button.
Sana Tayyeb
Sana Tayyeb 2015-3-22
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
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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回答（1 个）

Stephen23
Stephen23 2015-3-21
编辑：Stephen23 2015-3-21

4 个投票

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.

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