speed up the for and if loop

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Lavanya Ashokkumar
Lavanya Ashokkumar 2022-9-15
编辑： VBBV 2022-9-17
Hi,
I have a for and if loop that takes several hours to run. I tried to vectorize the for loop, but the main issue is the way I use the if statement in my script. Refering the array values at subscript is really important, because if i don't use the subscript the final values (melt) are incorrect. Is there way to speed-up my processing time, while taking care of the subscripts in a three dimensional array.
for i = 1:300
for j = 1:500
for k = 1:17000
if(temp(i,:) > 2)
melt(i,j,k) = temp(i,j,k) .* 3;
else
melt(i,j,k) = 0;
end
end
end
end
Thank you.

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回答（1 个）

VBBV
VBBV 2022-9-15
for i = 1:10:300 % use step increments
for j = 1:10:500
for k = 1:1000:17000
if(temp(i,:) > 2)
melt(i,j,k) = temp(i,j,k) .* 3;
else
melt(i,j,k) = 0;
end
end
end
end
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Lavanya Ashokkumar
Lavanya Ashokkumar 2022-9-16
Thanks for the reply. If I use increments in for loop, the skipped portions of the loop end up having zero values. Ultimately, this affects the final values of melt.
VBBV
VBBV 2022-9-17
编辑：VBBV 2022-9-17
I = 1:10:300;
J = 1:10:500
K = 1:1000:17000
for i = 1:length(I) % use step increments
for j = 1:length(J)
for k = 1:length(K)
if(temp(I(i),:) > 2)
melt(I(i),J(j),K(k)) = temp(I(i),J(j),K(k)) .* 3;
else
melt(I(i),J(j),K(k)) = 0;
end
end
end
end
An alternative way to avoid problem of zeros values in matrix can be done using above
% or use
melt(melt == 0) = []; % to get rid of zeros in the final matrix

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