Le lundi 21 décembre 2015 à 14:04 -0800, Joaquim Masset Lacombe Dias
Garcia a écrit :
> Why is the order of these loops barely affects the time?
Before doing this kind of comparison, you should ensure your code is
written to run efficiently. For that, you need to do
const N = 100
Else, the type of the variables isn't correctly inferred. Also, you
need to call the functions once to exclude compilation time from the
measurement.
After changing this (and fixing the name of the second argument for
cba), I get the maximum time difference between abc and cba, the latter
being 3x faster than the former (4x after adding @inbounds).
Regards
> N=100
> x=rand(N,N,N)
> y=rand(N,N,N)
>
> function abc(x::Array{Float64,3},y::Array{Float64,3})
> for a=1:N
> for b=1:N
> for c=1:N
> y[a,b,c]=x[a,b,c]
> end
> end
> end
> end
> function acb(x::Array{Float64,3},y::Array{Float64,3})
> for a=1:N
> for c=1:N
> for b=1:N
> y[a,b,c]=x[a,b,c]
> end
> end
> end
> end
> function bac(x::Array{Float64,3},y::Array{Float64,3})
> for b=1:N
> for a=1:N
> for c=1:N
> y[a,b,c]=x[a,b,c]
> end
> end
> end
> end
> function bca(x::Array{Float64,3},y::Array{Float64,3})
> for b=1:N
> for c=1:N
> for a=1:N
> y[a,b,c]=x[a,b,c]
> end
> end
> end
> end
> function cab(x::Array{Float64,3},y::Array{Float64,3})
> for c=1:N
> for a=1:N
> for b=1:N
> y[a,b,c]=x[a,b,c]
> end
> end
> end
> end
> function cba(x::Array{Float64,3},xx::Array{Float64,3})
> for c=1:N
> for b=1:N
> for a=1:N
> y[a,b,c]=x[a,b,c]
> end
> end
> end
> end
>
> @time abc(x,y)
> @time acb(x,y)
> @time bac(x,y)
> @time bca(x,y)
> @time cab(x,y)
> @time cba(x,y)
