How to increase the computation time of this code?

Question

Gopichandh Danala 2017-1-31

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/322731-how-to-increase-the-computation-time-of-this-code

评论： Gopichandh Danala 2017-2-3

Hi, I am working on computing some features of an image data set and saving the features for later use. Below is the code:

tic
l = 9907 % size of image data set
% pre-allocating space for variables in the for loop
Icolor = cell(1,l);
Iwave = cell(1,l);
IglrlFeatures = cell(1,l);
for i = 1:l % l = size of image data set = 9907
    IDB{1,i} = imread(strcat(path,strcat(num2str(i),'.jpg')));
    Icolor{1,i} = colorMoments(IDB{1,i}); % 6-features in each cell
    Iwave{1,i} = waveletTransform(IDB{1,i}); % 8-features in each cell
    IglrlFeatures{1,i}  = textureFeatures(IDB{1,i}); % 44-features in each cell
    ICW{1,i} = [Icolor{1,i} Iwave{1,i} IglrlFeatures{1,i}];
end
toc

Here the computation time for each function on single image is:

colorMoments(single_image) = Elapsed time is 0.009689 seconds.

waveletTransform(single_image) = Elapsed time is 0.018069 seconds.

textureFeatures(single_image) = Elapsed time is 0.022902 seconds.

l = data set size = 9907 images

Computational times for different data set sizes (l):

l = 10; Elapsed time is 0.402629 seconds.

l = 100; Elapsed time is 2.233971 seconds.

l = 1000; Elapsed time is 21.178395 seconds.

l = 2000; Elapsed time is 44.510071 seconds.

l = 5000; Elapsed time is 111.393866 seconds.

l = 9907; Elapsed time is 238.924998 seconds. approximately (~4 mins)

I want to decrease this computational time, any suggestions?

Thanks, Gopi

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Jan 2017-2-2

Please post the code and the error message.

Gopichandh Danala 2017-2-2

在 MATLAB Online 中打开

Here is the final code that is working:

Icolor = cell(1,l);
Iwave = cell(1,l);
idb = cell(1,l);
tic
parfor i = 1:l
    idb{1,i} = imread(strcat(p_address,strcat(num2str(i),'.jpg')));
    Icolor{1,i} = colorMoments(idb{1,i}); % 6-features in each cell
    Iwave{1,i} = waveletTransform(idb{1,i}); % 8-features in each cell
%     IglrlFeatures{1,i}  = textureFeatures(IDB{1,i}); % 44-features in each cell
%     ICW{1,i} = [Icolor{1,i} Iwave{1,i} IglrlFeatures{1,i}];
    icw{1,i} = [Icolor{1,i} Iwave{1,i}];
end
toc

I don't see much difference between this and above code, but maybe my previous error was because of some global variables inside my GUI functions. I think they messed it up.

Performace improvement:

for loop: 92secs

parfor loop: 31secs

Really helpful, But one last question when we start a parallel pool in Matlab2016, it starts 4 workers running what does it mean and does this number reflect performance speed. like if workers are more does it mean faster or increased performance

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Answer 1

Swaroop Mishra 2017-2-3

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/322731-how-to-increase-the-computation-time-of-this-code#answer_253158

Number of workers by default is equal to the number of cores in your system. You can change it inside Home-Parallel-Manage Cluster Profiles tab of MATLAB Toolstrip.

If you increase the number of workers, based on how parallel your algorithm can work, the performance can vary. There might be a bottleneck on sequential part of the algorithm. You might not be able to improve it.

If you have 4 workers, it does not mean that you will get exactly 4x speed as the sequential code. It means that you will get better computation speed for part of the code that is parallelizable.