Just checked the sparse matrix section of the Julia manual. My question
is whether what you explained only applies to actually declared sparse
matrix? In my case, the A is not declared as a sparse matrix even
though it has a lot of zeros in it - issparse(A) returns false.
On 2014年10月17日 15:03, Mauro wrote:
The operation A[i] for a sparse matrix is quite a bit more expensive
than for a dense array (where it is trivial). It first needs to convert [i]
it to a [k,m] index and then look it up in the sparse matrix. See:
https://github.com/JuliaLang/julia/blob/master/base/sparse/sparsematrix.jl#L841
However, if you just need to iterate over the non-zero values, it can
be done much more efficiently:
for nz in A.nzval
if abs(nz)>1.
val += (nz - s) * (x + y)
end
end
We should probably add an iterator to sparsematrix.jl which does that.
