dolfin team mailing list archive

[A Navaei <axnavaei@xxxxxxxxxxxxxx>]

2009/2/18 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;

I didn't know that g.vector() is supposed to initialise a vector? I
thought it would return one:

http://www.fenics.org/pub/documents/dolfin/dolfin-progr-reference/d2/d42/classdolfin_1_1Function.html#db09253826459af5460acd5e3f52ea78

Anyway, as long as it works, that's all I wanted to know.


-Ali

> --
> 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();
>> >> }
>> >>
>> >
>> >> _______________________________________________
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>> >> DOLFIN-dev@xxxxxxxxxx
>> >> http://www.fenics.org/mailman/listinfo/dolfin-dev
>> >
>> >
>> > -----BEGIN PGP SIGNATURE-----
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>> >
>> > _______________________________________________
>> > DOLFIN-dev mailing list
>> > DOLFIN-dev@xxxxxxxxxx
>> > http://www.fenics.org/mailman/listinfo/dolfin-dev
>> >
>> >
>> _______________________________________________
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>
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