For the following matrix
my_matrix = randn(10000, 1000)
using eachindex to access all elements is much slower than using ranges or
even for el in my_matrix, even though it says in the documentation
(http://docs.julialang.org/en/release-0.4/stdlib/arrays/#Base.eachindex)
that eachindex uses ranges for Arrays.
Some code and numbers:
julia> sum = 0.0
julia> @time for iter in eachindex(my_matrix)
sum += my_matrix[iter]
end
1.288944 seconds (50.00 M allocations: 915.519 MB, 3.36% gc time)
julia> sum = 0.0
julia> @time for i in 1:10000, j in 1:1000
sum += my_matrix[i,j]
end
0.681678 seconds (34.38 M allocations: 524.582 MB, 2.45% gc time)
julia> sum = 0.0
julia> @time for el in my_matrix
sum += el
end
1.063564 seconds (40.00 M allocations: 762.993 MB, 3.41% gc time)
Am I reading the documentation wrong, or is there something strange with
the matrix indexing? Because as it is, I don't see any benefit of using
anything different than simple ranges for manipulating matrices.
