dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

On 8 March 2012 12:36, Johan Hake <hake.dev@xxxxxxxxx> wrote:
> On Thu, Mar 8, 2012 at 12:40 PM, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
>> The obvious first step to simplifying dolfin:Array is to minimise its
>> use. Any objections to changing dolfin::Array to std::vector in the
>> GenericFoo abstract linear algebra classes?
>
> It is only GenericVector that uses Array at the moment. Are you
> thinking of changing all double* to std::vector too?
>
>> The consequence on the Python side will be copying of data. I don't
>> think that this is an issue since the interfaces are low-level and
>> only likely used from Python for prototyping or debugging. In such
>> cases, I would expect that other aspects of the Python overhead to
>> swamp to cost of the data copy.
>
> Where it makes sense I am inclined to keep the Array class, and even
> if get,set are low level functionalities they are something that
> potentially will be called many times.

Will they ever be called many times from Python in production code?
They will be called from low-level C++ code, but using std::vector
will make no difference in this case since it will be passed by
reference.

>  I do not have a benchmark
> telling you that it makes a difference, but from my perspective it
> doesn't make sense to change to std::vector just for the sake of it.
>

The point is to simplify dolfin::Array. The most important usage is in
GenericFunction::eval, in which case it has fixed length. It was the
usage of dolfin::Array in this context that Joachim picked up the
performance issue. I favour dolfin::Array being as simple as possible
and targeted to handle the call-back type situation in
GenericFunction::eval both efficiently and safely (from both Python
and C++).

Garth

> Johan
>
>> Garth
>>
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-- 
Garth N. Wells
Department of Engineering, University of Cambridge
http://www.eng.cam.ac.uk/~gnw20