dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Feb 16, 2009 at 12:31:32PM +0000, Garth N. Wells wrote:
> 
> 
> Anders Logg wrote:
> > On Mon, Feb 16, 2009 at 12:11:42PM +0000, Garth N. Wells wrote:
> >>
> >> Anders Logg wrote:
> >>> On Mon, Feb 16, 2009 at 11:44:04AM +0000, Garth N. Wells wrote:
> >>>> Anders Logg wrote:
> >>>>> On Mon, Feb 16, 2009 at 11:30:46AM +0000, Garth N. Wells wrote:
> >>>>>> 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;
> >>>>>>>
> >>>>>>>>>>>> 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.
> >>>>>>>
> >>>>>> It is if a MyFunction object is copied to a MyFunction object, which we 
> >>>>>> couldn't do before. My change made this possible.
> >>>>>>
> >>>>>> Garth
> >>>>> What's the point of that? It's like copying half a Function.
> >>>>>
> >>>> No, it's a copy.
> >>> Only when assigning between two MyFunction objects.
> >>>
> >>>>> If I do
> >>>>>
> >>>>>   v = w;
> >>>>>
> >>>>> I expect v to be in everything essential the same as w.
> >>>>>
> >>>> If you do
> >>>>
> >>>>    MyFuncion f0;
> >>>>    MyFunction f1 = f0;
> >>>>
> >>>> f0 and and f1 will be the same. The assignment operator is a separate story.
> >>> What if you do 
> >>>
> >>>   MyFunction f0;
> >>>   MyOtherFunction f1 = f0;
> >>>
> >>> ?
> >>>
> >> I expect that you'll get an error when you try to call eval().
> >>
> >> Garth
> > 
> > Not if MyOtherFunction has overloaded eval(). So then f1 might be
> > cos(x) although f0 is sin(x).
> >
> 
> True.
> 
> > So assignment from a user-defined function does not make sense unless
> > we interpolate.
> >
> 
> It does make 'code' sense, but it does open the door for errors on the 
> part of the user. The best solution may be to wind back the clock and 
> just not allow the copying of user-defined functions. The only 
> restriction imposed by this that I can think of is that a function can't 
> return a user-defined Function.

If at some point we really need it, it would require very little code
to fix assignment/copying of user-defined functions. We just need to
add a Function pointer and then in eval() write

  if (user_function)
     user_function->eval(...)

But it's a complication so we can wait until we really need it (or use
interpolation).

-- 
Anders

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