Le mercredi 27 janvier 2016 à 22:37 -0800, Christopher Alexander a
écrit :
> Try something like this:
>
> adjCloseMuVec = Vector{Float32}(nFullYears)
> or
> adjCloseMuVec = zeros(Float32, nFullYears)
>
> This will init a vector of the proper size. I think zeros is
> slightly faster, but someone can correct me if that is not the case.
Actually that's the other way around. zeros() is slower because it
needs to fill the array with zeros. You can check this with some very
simple benchmarking:
julia> f() = for i in 1:100000 adjCloseMuVec = Vector{Float32}(10000) end
f (generic function with 1 method)
julia> g() = for i in 1:100000 adjCloseMuVec = zeros(Float32, 10000) end
g (generic function with 1 method)
julia> @time f()
0.164794 seconds (202.00 k allocations: 3.731 GB, 52.40% gc time)
julia> @time f()
0.135390 seconds (200.00 k allocations: 3.731 GB, 52.57% gc time)
julia> @time g()
1.184917 seconds (201.75 k allocations: 3.731 GB, 10.57% gc time)
julia> @time g()
1.175267 seconds (200.00 k allocations: 3.731 GB, 10.38% gc time)
This overhead could be reduced/eliminated by using calloc, and could
even become the default, see
https://github.com/JuliaLang/julia/issues/9147
Given how high is the overhead, it looks like that change would be a
good idea.
Regards
> Chris
>
> On Thursday, January 28, 2016 at 1:26:09 AM UTC-5, Michael Landis
> wrote:
> > I am trying to compute some historical means and volatilities with
> > Julia, but I've been having some difficulty getting the
> > declarations and/or assignments right...
> >
> > When I try a declaration, like either of these:
> > adjCloseMuVec::Vector{Float32}; # or...
> > adjCloseMuVec::Vector{Float32,nFullYears};
> > I get: UndefVarError: adjCloseMuVec not defined
> >
> > When I try:
> > adjCloseMuVec = Vector{Float32}; # and later try:
> > reshape(adjCloseMuVec,nFullYears);
> > I get: MethodError: `reshape` has no method matching
> > reshape(::Type{Array{Float32,1}}, ::Int32)
> >
> > When I try:
> > adjCloseMuVec = Vector{Float32,nFullYears};
> > I get: too many parameters for type typealias
> >
> > So, the only acceptable path would seem to be:
> > adjCloseMuVec = Vector{Float32};
> > but when I later try:
> > adjCloseMuVec[curYr] = Float32(adjCloseMu); # or...
> > setindex!(adjCloseMuVec, Float32(adjCloseMu), curYr);
> > I get: MethodError: `setIndex!` has no method matching
> > setindex!(::Type{Array{Float32,1}}, ::Float32, ::Int64)
> >
> > So, I'm mystified as to the correct syntax. Any suggestions on an
> > acceptable way to declare a Vector of Int32 and load values into
> > it?
> >
