How to make a for faster?

Question

Oliver Lestrange 2020-8-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/586157-how-to-make-a-for-faster

编辑： Bruno Luong 2020-8-29

Hi,

I've the following code.

ix = ismember(idx_x(:),x(:));
iy = ismember(idx_y(:),y(:));
minimum = min(ix,iy);
for idx_=1:18:length(iy)
   for idx=1:18:length(ix)
       if minimum(idx)==1
           %index =[index;idx];
           altura_raio_direto = [altura_raio_direto; heights(idx)];
           % saber indices de heights que fazem parte do bresenham
       end
       iii = iii+1;
       disp(iii);
   end
end

heights is an array of 90 000 positions, as well as iy and ix.

How can I make this faster?

Thanks!

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Bruno Luong 2020-8-29

编辑：Bruno Luong 2020-8-29

You must think what is your double-loops are looping on. As long as you still see the need of double-loop you are completely off of understanding ISMEMBER and linear indexing.

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Answer 1

KSSV 2020-8-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/586157-how-to-make-a-for-faster#answer_486719

在 MATLAB Online 中打开

idx_=1:18:length(iy) ; 
idx=1:18:length(ix) ; 
if min(idx)==1
  altura_raio_direto = heights(idx) ;
end
altura_raio_direto = repmat(altura_raio_direto,1,length(idx_1)-1) ;

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Oliver Lestrange 2020-8-29

在 MATLAB Online 中打开

I am sorry, I forgot to mention what minimum is.

I've already edit the post.

minimum = min(ix,iy);

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Answer 2

Bruno Luong 2020-8-29

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/586157-how-to-make-a-for-faster#answer_486725

编辑：Bruno Luong 2020-8-29

在 MATLAB Online 中打开

ix = ismember(idx_x(:),x(:));
iy = ismember(idx_y(:),y(:));
ixy = ix & iy;
idx = 1:18:size(ixy,1);
altura_raio_direto = heights(idx(ixy(idx)));
%altura_raio_direto = repmat(altura_raio_direto,length(idx,1); % outer loop concatenate the same thing over and over