Thanks very much!
On Sunday, October 11, 2015 at 1:21:28 PM UTC+2, Tim Holy wrote:
>
> On Sunday, October 11, 2015 04:12:51 AM cheng wang wrote:
> > Hello everyone,
> >
> > I want to do an in-place tanh: y = tanh(x) assuming that y and x are
> > preallocated (both are Array{Float64, 1024*1024}).
> > I tested different implementations and got very different performance.
> >
> > Version1:
> > julia> @time map!(tanh, y, x)
> > 0.149988 seconds (3.15 M allocations: 48.000 MB, 1.24% gc time)
>
> Functions as arguments have a known performance overhead. See
> FastAnonymous.
>
> >
> > Version2:
> > julia> @time for i = 1:length(x)
> > y[i] = tanh(x[i])
> > end
> > 0.355105 seconds (5.24 M allocations: 95.984 MB, 1.83% gc time)
>
> Don't benchmark in global scope. Define a function that runs the loop for
> you.
>
> --Tim
>
> >
> > Version3: this one is not in-place, however it's the fast one.
> > julia> @time y += tanh(x)
> > 0.045402 seconds (10 allocations: 16.000 MB, 6.37% gc time)
> >
> > It's quite counterintuitive for me that version1 and version 2 are much
> > slower than version 3.
> > Can someone explain this a bit?
> >
> > Thanks!
> > Cheng
>
>
