MATLAB Answers


Replacing for loops for faster computations involving 3D matrix and sampling

Asked by Emily Her on 14 Oct 2018
Latest activity Edited by Bruno Luong
on 14 Oct 2018
Hi! I'm hoping there's someone out there who would give me an idea on how to increase computation speed for the following code:
for l=1:size(xSample,2) %%anisotropic 3D gaussian distribution of translation
for m=1:size(ySample,2) %%anisotropic 3D gaussian distribution of translation
for n=1:size(zSample,2) %%anisotropic 3D gaussian distribution of translation
shiftedDoseDist=imtranslate(doseDist,[xSample(l),ySample(m),zSample(n)]); %%3D image translation
shiftedDoseDist=imgaussfilt3(shiftedDoseDist,randomError); %%3D image blurring with Gauss filter
TCP_n(n)=prod(exp(-cellDensity.*vol.*exp(-alpha(q)*numOfFractions*dose- alpha(q)*numOfFractions*dose.^2/AlphaOnBeta+log(2)*T/tPot))); %%function I'm calculating
So what I'm trying to do is to get a bunch of different combinations of x,y,z from their respective Gaussian distributions for translation of a matrix doseDist (250x250x143), then a Gaussian filter is applied. Then with the resulting distribution, I compute something called TCP where the weighting of the Gaussian distribution is applied to get the expected value.
From the profiler, the bottleneck is in the imtranslate and imgaussfilt3 functions which I don't think they can be further optimised - basically left with getting rid of the nested for loops.
Any help would be appreciated!


what are the sizes of TCP_n,TCP_m &TCP_l??
There are 3 samples [1x3] for each x,y,z direction and there is another outer for loop which I didn't include (alpha(q)) which is samples [1x4]

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1 Answer

Answer by Bruno Luong
on 14 Oct 2018
Edited by Bruno Luong
on 14 Oct 2018

What are xSample,... zSample and idx?
Not sure you need to translate and filter over and over in the for-loop. It seems awfully wasteful to me.
Rather you could do the filtering once on the big image and extract the information (dose) at appropriate subindexing.


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