# Increasing the caclulation speed while using loops

1 view (last 30 days)
Hamid on 17 Nov 2022
Edited: Stephen23 on 18 Nov 2022
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?
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];
Stephen23 on 18 Nov 2022
Edited: Stephen23 on 18 Nov 2022
"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).

David Goodmanson on 17 Nov 2022
Edited: David Goodmanson on 17 Nov 2022
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')
Hamid on 18 Nov 2022
Hi David,
I see. Thanks a lot!

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