speed up the for and if loop

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.

Answer 1

[VBBV]

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

[VBBV]

oneway is you can use step increments in for loop to compute faster

[Lavanya Ashokkumar]

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]

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