How can I make this code faster?

Question

Sherwin 2016-12-27

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/318352-how-can-i-make-this-code-faster

评论： per isakson 2016-12-29

采纳的回答： per isakson

SA.mat

在 MATLAB Online 中打开

Hi, I have a cell array, like the attached image, named SA.

In each column of this array, I want to select the cells that are not empty, two by two (for eachmple if there are 3 cells in a column which are not empty, we have 3C2=3 selections, 1&2,1&3,2&3) and compare the elements of these two selected cells in a way that each element of the first cell is compared to all of the elements of the second selected cell then each time the absolute difference is less than 2 one unit is added to S. This is done for the second and rest of the elements of the first cell and when all of the nonempty cells in a column are compared the whole procedure is repeated for the next columns. I'm so sorry about the poor explanation. So here is my code for the aforementioned procedure, maybe it helps.

    S = 0;
    for p = 1:9    %Each Column of SA
        for b = 1:8 %Each Row of SA
            for  j = 1:8 % Another Row  
                if  j>b  %If the second selected row number is greater than the first
                    if numel(SA{b,p})~= 0 && numel(SA{j,p})~= 0   %and if none of the cells are empty
                        for  m = 1:numel(SA{b,p})  %select one element from the first cell
                            for n = 1:numel(SA{j,p}) % and one element from the second cell
                                if abs(SA{b,p}(m)- SA{j,p}(n)) <= 2  %if the difference is less than 2
                                    S = S +1;   % add one unit to S
                                end
                            end
                        end
                    end
                end
            end
        end
    end

As you can guess this code needs a lot of time to run. So are there any other faster ways to code this? Thank you so much in advance. P.S. There are 9 columns and 8 rows in SA. mat-file is atached.

2 个评论
显示无隐藏无

per isakson 2016-12-28

编辑：per isakson 2016-12-28

The chance to get an answer increases if you upload a mat-file, which contains SA
Am I correct that the input of your code is SA and the output is S ?

Sherwin 2016-12-28

编辑：Sherwin 2016-12-28

Thank you so much, yes you are right. S is calculated according to the SA array using the explained procedure. and, I'll attach it right away, thank you.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

per isakson 2016-12-28

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/318352-how-can-i-make-this-code-faster#answer_248698

编辑：per isakson 2016-12-28

在 MATLAB Online 中打开

I've done three things

Put the code in a function, because I'm more comfortable with functions than with scripts
Removed the references to cell arrays from the inner loops. That increases the speed an order of magnitude. See SAbp = SA{b,p};.
Vectorized the innermost loop, which doubles the speed.

function    [ S, S1 ] = cssm( SA )
    S  = 0;
    S1 = 0;
    for p = 1:9    %Each Column of SA
        for b = 1:8 %Each Row of SA
            SAbp = SA{b,p};
            for  j = 1:8 % Another Row  
                SAjp = SA{j,p};
                if  j>b  %If the second selected row number is greater than the first
                    if numel(SAbp)~= 0 && numel(SAjp)~= 0   %and if none of the cells are empty
                        for  m = 1:numel(SAbp)  %select one element from the first cell
%                             for n = 1:numel(SAjp) % and one element from the second cell
%                                 le2 = abs(SAbp(m)- SAjp(n)) <= 2;
%                                 if le2  %if the difference is less than 2
%                                     S = S +1;   % add one unit to S
%                                 end
%                             end
                            S1 = S1 + sum( double( abs( SAbp(m) - SAjp ) <= 2 ) );
                        end
                    end
                end
            end
        end
    end
end

Run with and without the innermost loop

>> tic, [ S, S1 ] = cssm( SA ), toc
S =
     0
S1 =
       19119
Elapsed time is 0.031820 seconds.

Note that tic,toc and profile show different results of the comparisons of speed between the different versions of the code. I think that's because the "JIT/Accelerator" is less aggressive when profile is running.