[julia-users] is for iteration very expensive?

[K Leo]

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
=============