dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

I understand your point. However, I just checked in some updates of
NewFunction that lets a user do

class MyFunction : NewFunctionExpression
{
    real operator()(const Point& p)
   {
       return sin(p.x);
   }
};

MyFunction f;

Could you take a look and see if you like the new/old solution?
It's not very complicated. The projection just checks if data is null
and in that case calls the user defined evaluation operator.

/Anders

On Mon, Feb 14, 2005 at 03:35:25PM +0100, Johan Jansson wrote:

> I'm thinking about how to enable user-defined functions, but I don't
> have a clear solution.
> 
> The idea right now seems to be to subclass NewFunction, a la:
> 
> // Source term
> // Example using NewFunction
> 
> class F : public NewFunction
> {
> public:
>   F(const Mesh& mesh, const NewFiniteElement& element, NewVector& x) :
>     NewFunction(mesh, element, x)
>   {
>   }
>   virtual real operator()(const Point& p)
>   {
>     real pi = DOLFIN_PI;
>     return 14.0 * pi*pi * sin(pi*p.x) * sin(2.0*pi*p.y) * sin(3.0*pi*p.z);
>   }
> };
> 
> We could have a separate constructor when an expression is given, and
> then project the given expression.
> 
> I think this is a bit ugly though, it seems unnecessarily complex.
> 
> Another solution would be to separate the expression out into a
> functor (function class), and the example would be:
> 
> class F : Expression
> {
>   virtual real operator()(const Point& p)
>   {
>     real pi = DOLFIN_PI;
>     return 14.0 * pi*pi * sin(pi*p.x) * sin(2.0*pi*p.y) * sin(3.0*pi*p.z);
>   }
> }
> 
> then:
> 
> int main()
> {
>   ...
> 
>   F fexpression;
>   NewFunction f(mesh, element, fexpression);
>   
>   ..
> }
> 
> This seems much more natural. When we have a function given by the
> values of its degrees of freedom, we pass a vector with the dofs to
> NewFunction. When we have a function given by an expression, we pass
> the expression to NewFunction and it projects it and stores it as
> values of the dofs. However, we would need to introduce a new class:
> Expression. What do you think?
> 
>   Johan
> 
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