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