How to increase the speed of this code?

Question

Zhongruo Wang 2016-4-9

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/278053-how-to-increase-the-speed-of-this-code

回答： Kuifeng 2016-4-9

Hi,

I write a script to check the lattice point the (vector pts), which is in the sphere centered at certain points(x and y) which is on the top side of the lattice. But this code works so slow which contains a lot of for loop and square root operation. Can you help me to fix this problem?

if true
  % vt = 0.4; 
pts1 = []
for i = 1:1:length(x)
  for j = 1:1:length(pts)
        dist = (x(i)-pts(j,1))^2+(y(i)-pts(j,2))^2+(pts(j,3))^2; 
        %distance from lattice to the seed
        if dist <= vt^2
            a = [pts(j,1) pts(j,2) -pts(j,3)];
            disp(a);
            pts1 = [pts1;a];
        end
    end
end  
end

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Answer 1

Kuifeng 2016-4-9

0
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https://ww2.mathworks.cn/matlabcentral/answers/278053-how-to-increase-the-speed-of-this-code#answer_217132

在 MATLAB Online 中打开

 % 1. use vectors instead of the for loop to calculate distance, example
dist = sqrt(x.-xCenter).^2.+(y.-yCenter).^2.+(z.-zCenter).^2);
% 2. use 'find' for criteria <=vt^2. make some changes to the two lines
find(dist <=vt^2).