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[Garth Wells <772787@xxxxxxxxxxxxxxxxxx>]

** Changed in: dolfin
   Importance: Undecided => Medium

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https://bugs.launchpad.net/bugs/772787

Title:
  Constant needs to overload eval(values,x)

Status in DOLFIN:
  Fix Committed

Bug description:
  The following example gives me an error. I can't figure out where the
  problem is in my cpp code. Is it because I am using GenericFunction?
  The eval function is overloaded! Any help would be appreciated.

  Thanks,
  Chaffra

    56 x = numpy.zeros(10)
  ---> 57 tau_n.compute_vertex_values(x,mesh)
       58 print x
       59 
  RuntimeError: *** Error: Missing eval() function (must be overloaded).

  
  ______________EXAMPLE____________

  from dolfin import *
  import numpy

  cppcode = """
  class Tau_n1 : public Expression
  {
  public:
      boost::shared_ptr<GenericFunction> vth;
      boost::shared_ptr<GenericFunction> total_doping;
      boost::shared_ptr<GenericFunction> nt_srh;
      double nref_srh;
      double sigma;
      double gamma;
     
      Tau_n1() : Expression() {}
      
      void eval(Array<double>& values, const Array<double>& x) const
      {
          double _vth = (*vth)(x[0],x[1],x[2]);
          double _nt_srh = (*nt_srh)(x[0],x[1],x[2]);
          double _nt = std::abs( (*total_doping)(x[0],x[1],x[2]) );
          
          if (_nt == 0){
              _nt = _nt_srh;
          }
          else{
              _nt = _nt_srh*std::pow(_nt/nref_srh,gamma);
          }
          values[0] = 1.0/(sigma*_nt*_vth);
      }
      
      void eval(Array<double>& values, const Array<double>& x,  const ufc::cell& cell) const
      {
          eval(values,x);
      }
  };
  """

  mesh = UnitInterval(11)
  Q = FunctionSpace(mesh,'CG',1)

  tau_n = Expression(cppcode=cppcode)
  tau_n.nt_srh = Constant(1e13)
  tau_n.total_doping = Function(Q)
  tau_n.vth = Constant(1.0)
  tau_n.nref_srh = 1e12
  tau_n.sigma = 1e-6
  tau_n.gamma = 1.76

  x = numpy.zeros(10)
  tau_n.compute_vertex_values(x,mesh)
  print x