dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Thursday 02 July 2009 23:22:35 Garth N. Wells wrote:
> Anders Logg wrote:
> > On Thu, Jul 02, 2009 at 01:42:41PM +0200, Johan Hake wrote:
> >> On Thursday 02 July 2009 13:24:28 Garth N. Wells wrote:
> >>> Johan Hake wrote:
> >>>> On Thursday 02 July 2009 13:07:47 Garth N. Wells wrote:
> >>>>> Marie Rognes wrote:
> >>>>>> Garth N. Wells wrote:
> >>>>>>> Marie Rognes wrote:
> >>>>>>>> The following code gives r = 0.0. It is not supposed to be.
> >>>>>>>>
> >>>>>>>> The problem seems to be that f's vector is still all zeros at the
> >>>>>>>> call to interpolate. Could this be easily fixed?
> >>>>>>>
> >>>>>>> This example should have led to an error message since f is not a
> >>>>>>> discrete function. I'll take a look.
> >>>>>>
> >>>>>> Ok, thanks!
> >>>>>>
> >>>>>> However,
> >>>>>>
> >>>>>> (a) Why is f not a discrete function? (It is defined on a finite
> >>>>>> element space?)
> >>>>>
> >>>>> On second thought, it may be a discrete function. I think that this
> >>>>> is defined in the Python interface and not the C++ interface, so I'll
> >>>>> take a look.
> >>>>
> >>>> A user defined function is not a discrete function untill you either
> >>>> call interpolate() or vector, also in python. The problem with the
> >>>> later is that you then create a vector which is initialized to 0.
> >>>>
> >>>> I think this has been discussed before, but should we populate the
> >>>> vector using f.interpolate() when vector is called on a userdefined
> >>>> function?
> >>>
> >>> Or perhaps Function::vector() should throw an error if the vector has
> >>> not already been allocated.
> >>
> >> I vote for this.
> >>
> >> The error message can include information about the user might want to
> >> call interpolate?
> >>
> >> Johan
> >
> > Sounds good.
>
> Unfortunately this won't work because we often do
>
>      Function u(V);
>      solve(A, u.vector(), b);

I see.

It would have worked in python though, as u would have been a discrete 
Function when created. However this is now implemented as a call to vector() 
in the constructor of DiscreteFunction, so that would also need some 
attention.

Johan

> Garth
>
> > Just to check: this only occurs (in Python) when a user defines a
> > Function using a C++ expression or overloads eval(), right?
> >
> >
> >
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