dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Feb 18, 2009 at 04:48:00PM +0000, A Navaei wrote:
> 2009/2/18 Anders Logg <logg@xxxxxxxxx>:
> > On Wed, Feb 18, 2009 at 02:04:35PM +0000, A Navaei wrote:
> >> 2009/2/17 Anders Logg <logg@xxxxxxxxx>:
> >> > On Tue, Feb 17, 2009 at 03:28:08PM +0000, Garth N. Wells wrote:
> >> >>
> >> >>
> >> >> A Navaei wrote:
> >> >> > The following minimal test for Function in c++ reveals some bugs. I
> >> >> > guess this example can help me with dealing with the current issues of
> >> >> > ImageFunction.
> >> >> >
> >> >> > (1) interpolate.py does not work when a Function is created in c++ and
> >> >> > wrapped (see comment [2]). It seems that the bug is originated from
> >> >> > the copy constructor (see comment [3])
> >> >> >
> >> >> > (2) In order to perform the interpolation, why is it necessary to
> >> >> > create another Function and then copy it?
> >> >> >
> >> >> > (3) Signature checkes seem not working properly (see comment [1]). The
> >> >> > signature-based assignments are error-prone anyway, why the
> >> >> > object-oriented approach is not used?
> >> >> >
> >> >>
> >> >> Signatures are used to permit reading/writing Functions to a file. They
> >> >> are indeed error prone, so I believe that we reached a consensus a short
> >> >> while ago that we would remove pre-compiled elements.
> >> >>
> >> >> Garth
> >> >
> >> > Instead of signatures, I'd recommend that you define a simple form
> >> > file for each of the different types of FunctionSpace you need, for
> >> > example:
> >> >
> >> >  element = FiniteElement("CG", "triangle", 1)
> >> >
> >> >  v = TestFunction(element)
> >> >  u = TrialFunction(element)
> >> >  a = v*u*dx
> >> >
> >> > If you put this in a file named My.form and compile it with FFC using
> >> > -l dolfin, you will get a class named MyFunctionSpace that you can
> >> > then instantiate using just a mesh:
> >> >
> >> >  MyFunctionSpace V(mesh);
> >> >
> >> > Create one form file for each of the different types of FunctionSpace
> >> > that you need, name the files to something suitable and use the
> >> > generated code. That way you won't need to worry about signatures,
> >> > dofmaps and finite elements.
> >>
> >> Effectively, I've been using the very same method all this time, it
> >> does not work.
> >
> > Yes, it does. It's used in about 20 of the demos.
> >
> >> The copy constructor fix never worked. I've been trying to explain
> >> this in many different ways, but the right attention was never paid to
> >> this. Let's see if the sandbox example can convince you this time.
> >>
> >> A Function instance still cannot be returned by reference (or value).
> >> Returning as shared_ptr seems to work initially, but eventually it
> >> generates segmentation fault -- see attached.
> >
> > Yes, it can. There's absolutely no problem to return a Function by
> > reference. See the updated sandbox demo.
> 
> That's correct. There are 2 Function assignment, one inside
> FunctionContainer ctor and the other in main(). I thought the latter
> was the problem, which was returned by referece, but the problem was
> initiated by the latter.
> 
> >
> > The only problem is when you want to copy a Function which is only
> > defined in terms of an eval() operator. In those cases the Function
> > cannot be copied.
> >
> > If you do the following:
> >
> > class MyFunction : public Function
> > {
> > public:
> >
> >  MyFunction(const FunctionSpace& V) : Function(V) {};
> >
> >  void eval(double* values, const double* x) const
> >  {
> >    values[0] = sin(x[0]);
> >  }
> > };
> >
> > MyFunction f(V);
> > Function g = f;
> >
> > Do you then expect g to return sin(x)? It would be possible to
> > implement this but it would require g to keep a pointer to f so that
> > the eval() in g may call the eval() in f.
> 
> In the that example, MyFunction was not of interest. I want
> FunctionContainer to have a member function of type Function which can
> be eventually initialised inside the class using an input
> FunctionSpace. Forget about user defined functions, let's make the
> problem as simple as possible. In FunctionContainer, the assignment in
> ctor does not work, see comment [1]:
> 
> class FunctionContainer
> {
> public:
>   FunctionContainer(const FunctionSpace& V)
>   {
>     _f = Function(V); // [1]
>   };
> 	
>   const Function& get_function()
>   {
>   message("returning");
>     return _f;
>   };
> protected:
>   Function _f;
> };
> 
> I hope you're not going to argue again that this is not a bug, but an
> expected behaviour.

Yes, this is expected behavior. What happens when you do

  _f = Function(V);

are the following two things:

1. The constructor in Function is called with V to create a
user-defined function with a missing eval operator (and no vector).

2. The assignment operator is called to assign that function to _f.

This won't work since what you are assigning from does not have a
vector.

The following will work:

  Function g(V);
  g.vector();
  _f = g;

-- 
Anders


> 
> -Ali
> >
> >
> >
> >>
> >> -Ali
> >>
> >> >
> >> >
> >> > -----BEGIN PGP SIGNATURE-----
> >> > Version: GnuPG v1.4.9 (GNU/Linux)
> >> >
> >> > iEYEARECAAYFAkma2rQACgkQTuwUCDsYZdHp4ACfSbCXc2FAulzIdDsKvhz/6EGV
> >> > aY4An0eyftGV3hxR3L25M9LPu3X7KFg+
> >> > =z1cY
> >> > -----END PGP SIGNATURE-----
> >> >
> >> > _______________________________________________
> >> > DOLFIN-dev mailing list
> >> > DOLFIN-dev@xxxxxxxxxx
> >> > http://www.fenics.org/mailman/listinfo/dolfin-dev
> >> >
> >> >
> >
> >> // Place for random tests
> >>
> >> #include <dolfin.h>
> >> #include "Poisson.h"
> >>
> >> using namespace dolfin;
> >>
> >> class MyFunction : public Function
> >> {
> >> public:
> >>
> >>   MyFunction(const FunctionSpace& V) : Function(V) {};
> >>
> >>   void eval(double* values, const double* x) const
> >>   {
> >>     message("Calling eval");
> >>     double dx = x[0] - 0.5;
> >>     double dy = x[1] - 0.5;
> >>     values[0] = 500.0*exp(-(dx*dx + dy*dy) / 0.02);
> >>   }
> >> };
> >>
> >> class FunctionContainer
> >> {
> >> public:
> >>   FunctionContainer(const FunctionSpace& V)
> >>   {
> >>     _f = Function(V);
> >>   };
> >>
> >>   const Function& get_function()
> >>   {
> >>     return _f;
> >>   };
> >> protected:
> >>   Function _f;
> >> };
> >>
> >>
> >> int main()
> >> {
> >>   UnitSquare mesh(2, 2);
> >>   PoissonFunctionSpace V(mesh);
> >>   MyFunction f(V);
> >>   Vector x;
> >>
> >>   message("Interpolating to another vector");
> >>   f.interpolate(x, f.function_space());
> >>   x.disp();
> >>
> >>   message("Interpolating to the function vector");
> >>   f.interpolate(f.vector(), f.function_space());
> >>   f.vector().disp();
> >>
> >>   message("Interpolating using initialising by an external function");
> >>   MyFunction f_(f);
> >>   f.interpolate(f_.vector(), f.function_space());
> >>   f.vector().disp();
> >>
> >>   message("Returning Function by reference");
> >>   FunctionContainer fc(V);
> >>   Function f2 = fc.get_function();
> >> }
> >>
> >
> >> _______________________________________________
> >> DOLFIN-dev mailing list
> >> DOLFIN-dev@xxxxxxxxxx
> >> http://www.fenics.org/mailman/listinfo/dolfin-dev
> >
> >
> > -----BEGIN PGP SIGNATURE-----
> > Version: GnuPG v1.4.9 (GNU/Linux)
> >
> > iEYEARECAAYFAkmcOUcACgkQTuwUCDsYZdE/tACghYR+pHvXwurxKi2rKdcAPrtr
> > XaEAnihNPT9ar+ZLx07ltK+uZM03Ntlc
> > =8wBa
> > -----END PGP SIGNATURE-----
> >
> > _______________________________________________
> > DOLFIN-dev mailing list
> > DOLFIN-dev@xxxxxxxxxx
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> >
> >
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