Why is My Code Running So Slowly?

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James on 25 Apr 2016
Commented: Walter Roberson on 29 May 2019
My code is running incredibly slow. I have it setup so that it plots every so often throughout the "For" loop, but the plotting is unusually slow. I cannot spot the problem in my code. At the end you will notice that I have it pausing for a brief period of time so that the plot can be viewed.
Thank You, JS
Walter Roberson
Walter Roberson on 29 May 2019
Whether swapping to SSD or hard disc occurs depends upon the operating system and system configuration. It is, however, typical that some swap to disc can happen, and that is rather slow.

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Accepted Answer

jgg on 26 Apr 2016
Edited: jgg on 26 Apr 2016
Try using the profiler, as per isakson recommends. This will give you an idea of what is taking up your time. MATLAB will use a paging system if it runs out of RAM on most systems, which is very slow but prevents crashing; I see that you use like 85% of my system memory here, which is about 8 GB so it would depend on your system.
I tried this with the code you sent, and it indicated that line 118 was the problem. It doesn't seem to need to be there, since your code should generate one anyways, so I just commented it out and the performance improved dramatically; for reference, after that change, this runs in about 31s on my system.
The plotting still seems to be the slowest part of your code. Perhaps it would be better to just save the data to be plotted, then perform the plotting at the end. I'm clear why it's quite so slow, but you do have a lot of points to plot.

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