Did you run the test in global scope? Does the following code show the same
performance characteristics?
=============
function test1(A, s, x, y)
for i=1:length(A)
if abs(A[i])>0.
val += (A[i] - s) * (x + y)
end
end
end
@time test1(A, s, x, y)
------------
function test2(A, s, x, y)
iA = findn(A)
for i=1:length(iA)
val += (A[iA[i]] - s) * (x + y)
end
end
@time test2(A, s, x, y)
=============
kl. 08:21:40 UTC+2 fredag 17. oktober 2014 skrev K leo følgende:
>
> I have a sparse array (roughly 1/5 filled say). If I simply loop
> through it, it is about 10 times slower than if I loop through only the
> nonzero elements. Compare the following codes, the first is 10 times
> slower, even with the multiplications.
>
> =============
> for i=1:length(A)
> if abs(A[i])>0.
> val += (A[i] - s) * (x + y)
> end
> end
> ------------
> iA = findn(A)
> for i=1:length(iA)
> val += (A[iA[i]] - s) * (x + y)
> end
> =============
>
