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[Garth Wells <gnw20@xxxxxxxxx>]

Garth Wells wrote:
> logg wrote:
>> On Wed, Oct 21, 2009 at 04:31:12PM -0000, Garth Wells wrote:
>>> oelgaard wrote:
>>>> Quoting Garth Wells <gnw20@xxxxxxxxx>:
>>>>
>>>>> oelgaard wrote:
>>>>>> Public bug reported:
>>>>>>
>>>>>> The following two files will reproduce the bug.
>>>>>>
>>>>>> M.ufl:
>>>>>>
>>>>>> exact = FiniteElement("Lagrange", triangle, 6)
>>>>>> approx = FiniteElement("Lagrange", triangle, 1)
>>>>>>
>>>>>> u = Function(exact)
>>>>>> uh = Function(approx)
>>>>>>
>>>>>> M = (uh - u)*(uh - u)*dx
>>>>>>
>>>>>>
>>>>>> main.cpp:
>>>>>>
>>>>>> #include <dolfin.h>
>>>>>> #include "M.h"
>>>>>>
>>>>>> using namespace dolfin;
>>>>>>
>>>>>> class Expr : public Expression
>>>>>> {
>>>>>> public:
>>>>>>
>>>>>>   Expr() : Expression(2) {}
>>>>>>
>>>>>>   void eval(double* values, const double* x) const
>>>>>>   {
>>>>>>     values[0] = 10*x[0]*x[1];
>>>>>>   }
>>>>>>
>>>>>> };
>>>>>>
>>>>>> class Expr2 : public Expression
>>>>>> {
>>>>>> public:
>>>>>>
>>>>>>   Expr2() : Expression(2) {}
>>>>>>
>>>>>>   void eval(double* values, const double* x) const
>>>>>>   {
>>>>>>     values[0] = sin(5*x[0]);
>>>>>>   }
>>>>>> };
>>>>>>
>>>>>> class Func2 : public Function
>>>>>> {
>>>>>> public:
>>>>>>
>>>>>>   Func2(FunctionSpace& v) : Function(v) {}
>>>>>>
>>>>>>   void eval(double* values, const double* x) const
>>>>>>   {
>>>>>>     values[0] = sin(5*x[0]);
>>>>>>   }
>>>>>> };
>>>>>>
>>>>> The above class shouldn't be possible with the development version of
>>>>> DOLFIN. Are you using an older version?
>>>> Yes:
>>>>
>>>> changeset:   7392:70596970a173
>>>> tag:         tip
>>>> user:        Anders Logg <logg@xxxxxxxxx>
>>>> date:        Wed Oct 21 17:34:32 2009 +0200
>>>> summary:     Attempt at bug fix in application of periodic boundary conditions
>>>> on
>>>>
>>>>
>>>> Why shouldn't it be possible to derive a class from Function?
>>>>
>>> In the new design, Function is strictly a finite element function, and
>>> not a user-defined function. We may need to fix something to make it
>>> impossible to create a Function with a user-provided eval(..).
>>> Expression should be used instead.
>> I don't see how to do this. The eval function is virtual so there's
>> nothing "wrong" with overloading it.
>>
>> Unless there's some trick we can do with making it private or
>> protected in Function.
>>
> 
> It should be made private.
> 

Actually, that won't work so it's up to the user to use Function 
correctly. The Function eval functions are not virtual, so that should 
be a hint.

Garth

> Garth
> 
>> --
>> Anders
>>
>>
>>>>>>          Status: New
>>>>>>
>>>>> Status in DOLFIN: New
>>>>>
>>>>> Bug description:
>>>>> The following two files will reproduce the bug.
>>>>>
>>>>> M.ufl:
>>>>>
>>>>> exact = FiniteElement("Lagrange", triangle, 6)
>>>>> approx = FiniteElement("Lagrange", triangle, 1)
>>>>>
>>>>> u = Function(exact)
>>>>> uh = Function(approx)
>>>>>
>>>>> M = (uh - u)*(uh - u)*dx
>>>>>
>>>>>
>>>>> main.cpp:
>>>>>
>>>>> #include <dolfin.h>
>>>>> #include "M.h"
>>>>>
>>>>> using namespace dolfin;
>>>>>
>>>>> class Expr : public Expression
>>>>> {
>>>>> public:
>>>>>
>>>>>   Expr() : Expression(2) {}
>>>>>
>>>>>   void eval(double* values, const double* x) const
>>>>>   {
>>>>>     values[0] = 10*x[0]*x[1];
>>>>>   }
>>>>>
>>>>> };
>>>>>
>>>>> class Expr2 : public Expression
>>>>> {
>>>>> public:
>>>>>
>>>>>   Expr2() : Expression(2) {}
>>>>>
>>>>>   void eval(double* values, const double* x) const
>>>>>   {
>>>>>     values[0] = sin(5*x[0]);
>>>>>   }
>>>>> };
>>>>>
>>>>> class Func2 : public Function
>>>>> {
>>>>> public:
>>>>>
>>>>>   Func2(FunctionSpace& v) : Function(v) {}
>>>>>
>>>>>   void eval(double* values, const double* x) const
>>>>>   {
>>>>>     values[0] = sin(5*x[0]);
>>>>>   }
>>>>> };
>>>>>
>>>>> int main()
>>>>> {
>>>>>   // Create mesh and function space
>>>>>   UnitSquare mesh(8, 8);
>>>>>   M::CoefficientSpace_u Vu(mesh);
>>>>>   M::CoefficientSpace_uh Vuh(mesh);
>>>>>
>>>>>   Expr exact;
>>>>> //  Expr2 approx;      // 12.5251
>>>>> //  Func2 approx(Vuh); // 11.1111
>>>>>   Func2 approx(Vu);    // 11.1111
>>>>>
>>>>>   M::Functional m(mesh);
>>>>>   m.u = exact;
>>>>>   m.uh = approx;
>>>>>
>>>>>   double error = assemble(m);
>>>>>
>>>>>   std::cout << "error: " << error << std::endl;
>>>>>
>>>>>   return 0;
>>>>> }
>>>>>
>

-- 
function and expression does not give the same result
https://bugs.launchpad.net/bugs/457262
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Status in DOLFIN: New

Bug description:
The following two files will reproduce the bug.

M.ufl:

exact = FiniteElement("Lagrange", triangle, 6)
approx = FiniteElement("Lagrange", triangle, 1)

u = Function(exact)
uh = Function(approx)

M = (uh - u)*(uh - u)*dx


main.cpp:

#include <dolfin.h>
#include "M.h"

using namespace dolfin;

class Expr : public Expression
{
public:

  Expr() : Expression(2) {}

  void eval(double* values, const double* x) const
  {
    values[0] = 10*x[0]*x[1];
  }

};

class Expr2 : public Expression
{
public:

  Expr2() : Expression(2) {}

  void eval(double* values, const double* x) const
  {
    values[0] = sin(5*x[0]);
  }
};

class Func2 : public Function
{
public:

  Func2(FunctionSpace& v) : Function(v) {}

  void eval(double* values, const double* x) const
  {
    values[0] = sin(5*x[0]);
  }
};

int main()
{
  // Create mesh and function space
  UnitSquare mesh(8, 8);
  M::CoefficientSpace_u Vu(mesh);
  M::CoefficientSpace_uh Vuh(mesh);

  Expr exact;
//  Expr2 approx;      // 12.5251
//  Func2 approx(Vuh); // 11.1111
  Func2 approx(Vu);    // 11.1111

  M::Functional m(mesh);
  m.u = exact;
  m.uh = approx;

  double error = assemble(m);

  std::cout << "error: " << error << std::endl;

  return 0;
}