dolfin team mailing list archive

[A Navaei <axnavaei@xxxxxxxxxxxxxx>]

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;

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();
>> }
>>
>
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>> DOLFIN-dev@xxxxxxxxxx
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>
>
> -----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
> 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() : Function() {};
  
  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)
  {
    message("assigning function");
    MyFunction g(V);
    g.vector();
    _f = g;
  };
	
  const MyFunction& get_function()
  {
    message("returning");
    return _f;
  };
protected:
  MyFunction _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("Function container");
  FunctionContainer fc(V);
  Function f2 = fc.get_function();
  f2.interpolate(f2.vector(), f2.function_space());
  f2.vector().disp();
  //plot(f2);
}