speed up a for loop

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

Answer 1

[Walter Roberson]

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

[Giacomo Abrardo]

thank you very much