Increasing the caclulation speed while using loops

Question

Hamid 2022-11-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1853338-increasing-the-caclulation-speed-while-using-loops

编辑： Stephen23 2022-11-18

采纳的回答： David Goodmanson

data.mat

在 MATLAB Online 中打开

Dear MATLAB experts,

I considered a range for x and y and if x1 and y1 are within a specific range the code must convert x1 and y1 to the mean value of the specific range.

In other words, considering a pixel and if the values of x and y are inside the pixel, I wanted to replace the values with the position of the center of the pixel as shown in the attached file (if x and y are black corss must be replaced with red one)

Code is working but as the data is very big, the calculation speed is slow. Is there any modifications that may lead to increase the speed of calculations?

Thank you in advance.

data = load('data.mat').out1_com;
det_x        = 50;  
det_y        = 50; 
det_ch = 16;
%%
xedges = -(det_x/2):(det_x/det_ch):(det_x/2);
yedges = -(det_y/2):(det_y/det_ch):(det_y/2);
kf   =  data(:,1);
x1   =  data(:,2);
y1   =  data(:,3);
z1   =  data(:,4);
len  =  length(x1);
x11  =  zeros(len,1);
y11  =  zeros(len,1);
for  k=1:length(x1)
    for i = 1:length(xedges)-1
         for j = 1:length(yedges)-1
             idx1 = (xedges(i) <= x1(k)) & ((x1(k)) < xedges(i+1)) & (yedges(j) <= (y1(k))) & ((y1(k)) < yedges(j+1));
             if (idx1 == 1)
                 x11(k)=(xedges(i)+xedges(i+1)) ./ 2;
                 y11(k)=(yedges(j)+yedges(j+1)) ./ 2;
             end
         end
    end  
end
pos=[kf,x11,y11,z1];

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Hamid 2022-11-18

@Stephen23 Thank you so much for your comment. The problem is I don't want to count the points in each pixel and want to replace the values with mean value of edges.

Stephen23 2022-11-18

编辑：Stephen23 2022-11-18

"The problem is I don't want to count the points in each pixel "

You would use the 4th and 5th outputs (bin indices), not the 1st and 2nd outputs (counts).

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Answer 1

David Goodmanson 2022-11-17

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1853338-increasing-the-caclulation-speed-while-using-loops#answer_1102248

编辑：David Goodmanson 2022-11-17

在 MATLAB Online 中打开

Hi Hamid,

Hi Hamid, I have not speed checked this but it should be faster (the range in your example is different from the drawing).

det_x        = 50;  
det_y        = 50; 
det_ch = 16;
%
xedges = -(det_x/2):(det_x/det_ch):(det_x/2)
yedges = -(det_y/2):(det_y/det_ch):(det_y/2);
xmid = (xedges(1:end-1)+xedges(2:end))/2;
ymid = (yedges(1:end-1)+yedges(2:end))/2;
x = -25+50*rand(1,2000);                  % some data in -25< x,y <25
y = -25+50*rand(1,2000);
xr = round((x+25)*16/50 +1/2);
yr = round((y+25)*16/50 +1/2);
xnew = (xr-1/2)*50/16-25;
ynew = (yr-1/2)*50/16-25;
plot(x,y,'.',xnew,ynew,'o')

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David Goodmanson 2022-11-18

Hi Hamid,

I guess you are really asking only about xmid and ymid, since you defined xedges and yedges. I was going to use xmid, ymid to verify that the xnew and ynew arrays were ending up with the right values, but I realized that xnew and ynew were doing the right thing so I never used the check.

Hamid 2022-11-18