Great, thank you.
On Friday, December 19, 2014 6:37:03 PM UTC, John Myles White wrote:
>
> The problem is that your let block is not a proper function body. You need
> to time things inside of a function body:
>
> julia> function foo()
> @time a1 = zeros(Int64,10000000)
> @time resize!(a1, 1000)
> @time resize!(a1, 10000000)
> @time resize!(a1, 10000000)
> @time resize!(a1, 20000000)
> end
> foo (generic function with 1 method)
>
> julia> foo()
> elapsed time: 0.039935728 seconds (80000048 bytes allocated)
> elapsed time: 8.61e-6 seconds (0 bytes allocated)
> elapsed time: 4.45e-7 seconds (0 bytes allocated)
> elapsed time: 2.71e-7 seconds (0 bytes allocated)
> elapsed time: 0.000365734 seconds (160000000 bytes allocated)
>
> -- John
>
> On Dec 19, 2014, at 1:34 PM, John Drummond <joh...@gmail.com <javascript:>>
> wrote:
>
> > 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
> >
> > 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
> >
>
>
