This code seems to be (about 50%) faster than recursive functions:
Base.:+{N}(a::NTuple{N}, b::NTuple{N}) = ntuple(i -> a[i] + b[i], N)
But this seems (about 50%) slower:
((a[i] + b[i] for i = 1:N)...)
Anyway, I can use the first method, until I find something faster. It's
definitely way more convenient. Thanks.
Bill.
On 10 August 2016 at 16:56, Erik Schnetter <schnet...@gmail.com> wrote:
> The built-in type `CartesianIndex` supports adding and subtracting, and
> presumably also multiplication. It is implemented very efficiently, based
> on tuples.
>
> Otherwise, to generate efficient code, you might have to make use of
> "generated functions". These are similar to macros, but they know about the
> types upon which they act, and thus know the value of `N`. This is a bit
> low-level, so I'd use this only if (a) there is not other package
> available, and (b) you have examined Julia's performance and found it
> lacking.
>
> I would avoid overloading operators for `NTuple`, and instead us a new
> immutable type, since overloading operations for Julia's tuples can have
> unintended side effects.
>
> -erik
>
>
> On Wed, Aug 10, 2016 at 9:57 AM, 'Bill Hart' via julia-users <
> julia-users@googlegroups.com> wrote:
>
>> Does anyone know an efficient way to add NTuples in Julia?
>>
>> I can do it using recursive functions, but for various reasons this is
>> not efficient in my context. I really miss something like tuple(a[i] + b[i]
>> for i in 1:N) to create the resulting tuple all in one go (here a and b
>> would be tuples).
>>
>> The compiler doesn't do badly with recursive functions for handling
>> tuples in very straightforward situations, but for example, if I want to
>> create an immutable type based on a tuple the compiler doesn't seem to be
>> able to handle the necessary optimisations. At least, that is what I infer
>> from the timings. Consider
>>
>> immutable bill{N}
>> d::NTuple{N, Int}
>> end
>>
>> and I want to add two bill's together. If I have to add the tuples
>> themselves using recursive functions, then I no longer seem to be able to
>> do something like:
>>
>> A[i] = B[i] + C[i] efficiently, where A, B and C are arrays whose
>> elements are of type bill.
>>
>> I know how to handle tuples via arrays, but for efficiency reasons I
>> certainly don't want to do that, e.g. tuple([a[i] + b[i] for i in 1:N]...).
>>
>> Bill.
>>
>
>
>
> --
> Erik Schnetter <schnet...@gmail.com> http://www.perimeterinstitute.
> ca/personal/eschnetter/
>
