dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Monday 16 February 2009 12:06:09 Anders Logg wrote:
> On Mon, Feb 16, 2009 at 11:52:54AM +0100, Johan Hake wrote:
> > On Monday 16 February 2009 11:31:36 Anders Logg wrote:
> > > On Mon, Feb 16, 2009 at 10:12:21AM +0000, Garth N. Wells wrote:
> > > > Anders Logg wrote:
> > > > > On Mon, Feb 16, 2009 at 10:36:52AM +0100, Johan Hake wrote:
> > > > >> On Sunday 15 February 2009 21:23:44 DOLFIN wrote:
> > > > >>> One or more new changesets pushed to the primary dolfin
> > > > >>> repository. A short summary of the last three changesets is
> > > > >>> included below.
> > > > >>>
> > > > >>> changeset:   5701:d3661203791d9c7707695c59adbbd3a2e20a220c
> > > > >>> tag:         tip
> > > > >>> user:        Anders Logg <logg@xxxxxxxxx>
> > > > >>> date:        Sun Feb 15 21:23:36 2009 +0100
> > > > >>> files:       dolfin/function/Function.cpp
> > > > >>> description:
> > > > >>> Move code from Function copy constructor to assignment operator
> > > > >>> and call assignment operator from copy constructor
> > > > >>
> > > > >> I liked Garth solution better.
> > > > >>
> > > > >>  1) A copy constructor that, just copies the Function if it has
> > > > >>     a FunctionSpace.
> > > > >>  2) The assignment operator works only for discrete Functions.
> > > > >>
> > > > >> We could add an interpolate() (or something) function that
> > > > >>
> > > > >>   v.interpolate(*_vector, *_function_space);
> > > > >
> > > > > We already have exactly such a function.
> >
> > Do we?
>
> Yes:
>
>   /// Interpolate function to given function space
>   void interpolate(GenericVector& coefficients, const FunctionSpace& V)
> const;

Can you use this to initialize your own vector if you e.g. is a user-defined 
Function? I think we have ahd this discussion before, and Martin added such a 
function, but removed it because it was not general enough, or am I wrong?

> > > > >> Then the user can explicitly create a discrete function of its
> > > > >> user-defined Function. Now the user gets this as an implicitly
> > > > >> result of a function copy, which make litle sense to me.
> > > > >>
> > > > >> But that's just me :)
> > > > >
> > > > > I like it. Other opinions?
> > > >
> > > > It is neat, but I would prefer any interpolation to be more explicit
> > > > so that it's clear what's going on. A copy should be a straight copy.
> > > >
> > > > Garth
> > >
> > > ok. I've changed it back. See if it looks ok.
> >
> > Now a user cannot copy a Function that is not a discrete function, which
> > was the case before we started all this.
>
> Wasn't that the point? It's not possible to copy the eval() operator.
>
> Well it is but then it would be necessary to keep a pointer to the
> given Function and propagate the eval call to that Function's eval.
> That seems a bit overkill.
>
> > Also sometimes a copy is something different than an assignment, so it is
> > not always meaningfull to use *this = other; in the copy constructor.
>
> I've found it's almost always the case that one can implement the
> copy constructor by
>
>   *this = other;
>
> We use this in a bunch of other places, including the Mesh class.
>
> In which cases will it break?

I am thinking very simple here, it deals with defining a sane and complete C++ 
interface to Function. Should we be able to copy a user-defined Function or 
not? 

I thought yes, and no one came with any argument why not. Remember that this 
came from the discussion of returning a user-defined Function by value from 
an other function.

we are talking about

  MyFunc f(V);
  MyFunc g(f);

not

  MyFunc f(V);
  Function g(f);
  
So the logic is that a user-defined Function should stay the same if it is 
copied and the assignment operator can only be used for discrete functions. 

If we want to be able to copy a user-defined function without initializing the 
_vector, then the assignment operator needs to be different from the copy 
constructor.

Johan