[dune-fem] LocalFunctionAdapter

[Andreas Dedner]

Sorry about the confusion - I forgot the name change to
GridFunctionAdapter.

Martin already mentioned the performance issue - depending on
the space getting a local function is not that cheap. Having the
lambda option with global functions is nice and I would like to see
that integrated in dune-fem.
Best
Andreas


On 05/06/15 14:00, Martin Nolte wrote:
> Hi Macro,
>
> first of all, thank you very much for integrating the information into 
> the documentation. Few people bother to update it.
>
> As for your AnalyticalFunctionAdapter: I have such a thing myself 
> (called SimpleGridFunction), so I do think it is useful (especially 
> when used on a lambda expression).
>
> It should, however, be remembered that such a simple grid function 
> tends to be slow. Consider the following lambda:
>
> [ &u ] ( const Entity &e, const DomainType &x )
> {
>   RangeType v;
>   u.localFunction( entity ).evaluate( x, v );
>   return v;
> }
>
> Here, for each evaluation the degrees of freedom of the discrete 
> function u must be fetched from the global DofVector. Therefore, we 
> have to ask whether this is the correct concept.
>
> Personally, like the simplicity and, being aware of the performance 
> pitfall, I do not use it in performance critical sections. But for 
> initialization, data-i/o, or plain testing this is a great tool.
>
> But: Using a LocalFunctionAdapter is not so much code, either. And 
> this class does not automatically suffer from a performance impact.
>
> Best,
>
> Martin
>
>
>
> On 06/05/2015 02:24 PM, Agnese, Marco wrote:
>> Hi Andreas,
>> to recap the class LocalAnalyticalFunction which I implemented simply 
>> store a reference to a C++ function
>>
>> RangeType f(const DomainType& x,const double& t,const EntityType& 
>> entity)
>> {
>>   //do stuff
>> }
>>
>> and add all the necessary types/methods in such a way you can pass it 
>> to the LocalFunctionAdpater to obtain a GridFunction.
>>
>> I would like to add a class AnalyticalFunctionAdapter do Dune-Fem 
>> that takes a C++ function and return a GridFunction (using the 
>> aforementioned LocalAnalyticalFunction and LocalFunctionAdapter).
>>
>> In this way would be very handy for everybody to transform the c++ 
>> fucntion f into a GridFunction.
>>
>> Cheers,
>> Marco.
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>>
>