dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Wednesday 18 February 2009 20:56:59 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.
> >
> > 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.
>
> Yes, we eventually want to get the image data in eval() and obviously
> the work around:
>
>  Function g(V);
>  g.vector();
>  _f = g;

I haven't fully followed the thread, so I might say somthing that has already 
been mentioned, but shouldn't the approach used in interpolate.py work?

  class FunctionContainer
  {
  public:
    FunctionContainer(const FunctionSpace& V):_f(V)
    {
      message("assigning function");
      MyFunction g(V);
      g.interpolate(_f.vector(),V);
    };
	
    const Function& get_function()
    {
      message("returning");
      return _f;
    };
  protected:
    Function _f;
  };

Here g's vector is never initialized and the eval function is used to 
interpolate to the vector of _f.

Johan

> does not call eval(). I don't think if it is possible to do this
> without amending the Function class? The denial of changing the
> visibility of the member variables to protected is making this
> unnecessarily more and more complicated. I am attaching the updated
> sandbox test.
>
>
> -Ali
>
> > --
> > Anders
> >
> >> -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-----
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> > =8wBa
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> >
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