speed up a for loop

Question

Giacomo Abrardo 2021-4-18

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评论： Giacomo Abrardo 2021-4-18

Hi i have a double foor loop like this where N3=1376 and N1=498.

I need to speed up the double loop because in one day of running i just have a 1376*68 matrix. The first solution i considered is to preallocate the matrix SM outside the double loop but i don't know if that will be enough. Do you have any suggestions? Thanks all

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Answer 1

Walter Roberson 2021-4-18

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https://ww2.mathworks.cn/matlabcentral/answers/805921-speed-up-a-for-loop#answer_678316

编辑：Walter Roberson 2021-4-18

在 MATLAB Online 中打开

Inside your inner for loop, you read three .nc files. For efficiency, you need to reduce the number of files you need. So reverse the order of your loops

for j = 1 : N3
   FileNC=P{j}
   ncdisp(FileNC);
   latidudine = ncread(FileNC, 'lat');
   longitudine = ncread(FileNC, 'lon');
   umidata = ncread(FileNC, 'ssm');
   do the two find and through to sm=sm*0.5
   for k = 1 : N1
       LAT = Latitudine_stazioni(k,1);
       LONG = Lognitudine_stazioni(k,1);
       [val1,idx1] = min(abs(Long-LONG));
       and through to the end of your loop, to the assigment to SM(j,k)
   end
end