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On Thursday, July 31, 2014 4:39:26 PM UTC-4, Iain Dunning wrote:
>
> 1. Yes, it would create an array of pointers.
> 2. Yes, it would worsen performance.
> 3. Try using a Tuple, e.g.
>
> julia> immutable Dual{T1,T2,N}
> x::T1
> dx::NTuple{N,T2}
> end
>
> julia> Dual(1.0, (2.0, 3.0))
> Dual{Float64,Float64,2}(1.0,(2.0,3.0))
>
> I think this will be stored "flat" but I'm not 100% sure.
>
> On Thursday, July 31, 2014 2:45:27 AM UTC-4, Philippe Maincon wrote:
>>
>> Hi,
>>
>> Say I create a multidimensional array "a" and I have defined the type
>>
>>
>> immutable Dual{T1,T2} # immutable: fields are read only, except by
>> constructor
>>
>> x ::T1 # think of this as a Float for this discussion
>>
>> dx::T2 # Vector{Float}
>>
>> end
>>
>>
>> (yes, I am playing with automatic differentiation) Then I want to do the
>> following allocation:
>>
>>
>> b = Array(Dual{Float64, Array{Float64,ndims(a)}} ,size(a)...)
>>
>>
>> So I want an array of "structures", each having as field a Float, and an
>> Array. This would be accessed as b[i].x and b[i].dx[j]
>>
>> Now my intention is that all these dx array *have the same size*, which
>> opens for packed storage, without any use of pointers by the compiler.
>> This, I understand is what "immutable" is for, and is exploited, implicitly,
>> in Complex.jl. However, in my declaration above, I do not spec the size of
>> the dx's, and sothis will compile, I believe, into an array of x's and
>> pointer to dx's, and I expect suboptimal performance.
>>
>>
>> 1. Am I right that this would compile into an array of pointers?
>> 2. If yes, am I right that this would cause poor performance? (think of
>> Complex,jl, you really want things to go fast, there)
>> 3. If yes, is there a way to allocate b that ensures "packed storage"?
>>
>>
>> Thank you beforehand for your answer, but most of all, thank you for Julia!
>>
>>
>> Philippe
>>
>>
