dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

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);

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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