Sorry to be stupid - but this also helps me understand things for another
question:
So bytes allocated would be the underlying usage of memory.
in which case with
julia> let
@time a1 = zeros(Int64,10000000)
@time resize!(a1, 1000)
@time resize!(a1, 10000000)
@time resize!(a1, 10000000)
@time resize!(a1, 20000000)
end
elapsed time: 0.015554722 seconds (80000152 bytes allocated)
elapsed time: 5.735e-6 seconds (80 bytes allocated)
elapsed time: 2.113e-6 seconds (80 bytes allocated)
elapsed time: 2.113e-6 seconds (80 bytes allocated)
elapsed time: 0.027380439 seconds (160000080 bytes allocated)
20000000-element Array{Int64,1}:
what's the 80 bytes allocated when I'm just changing the length I'm using?
And will increasing the size beyond the maximum always copy the whole array?
Many thanks for clarifying this.
On Friday, December 19, 2014 6:12:42 PM UTC, Tim Holy wrote:
>
> Julia's arrays grow by doubling, see
> http://en.wikipedia.org/wiki/Dynamic_array
> <http://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FDynamic_array&sa=D&sntz=1&usg=AFQjCNFN_QdkMYGq1dw8WSUnyhk_tWSFfg>
>
>
> Since you're appending elements to an array, julia has to have somewhere
> to
> put them---and when there's no spare capacity, julia has to allocate a new
> array and copy the entire thing. So some allocations are much bigger than
> what
> you're adding, but others (as you can see) are 0.
>
> This is a marked improvement over Matlab, which makes a copy of your
> entire
> array each time you add 1 element.
>
> Best,
> --Tim
>
> On Friday, December 19, 2014 10:00:28 AM John Drummond wrote:
> > For the following code (julia 0.3.3 in windows 7 ) I don't understand
> what
> > the bytes allocated in @time means
> >
> > All I'm doing each time is adding 10 8 byte integers
> >
> > Thanks for any thoughts
> >
> > julia> @time c = [1,2]
> > elapsed time: 3.32e-6 seconds (144 bytes allocated)
> > 2-element Array{Int64,1}:
> > 1
> > 2
> >
> > julia> sizeof(c)
> > 16
> >
> >
> > julia> @time for x in 30:39 push!(c, x) end
> > elapsed time: 2.717e-6 seconds (256 bytes allocated)
> >
> > julia> @time for x in 30:39 push!(c, x) end
> > elapsed time: 2.717e-6 seconds (288 bytes allocated)
> >
> > julia> @time for x in 30:39 push!(c, x) end
> > elapsed time: 2.112e-6 seconds (0 bytes allocated)
> >
> > julia> @time for x in 30:39 push!(c, x) end
> > elapsed time: 3.321e-6 seconds (640 bytes allocated)
> >
> > julia> sizeof(c)
> > 336
>
>
