text: // This is core/vnl/vnl_cost_function.h
  #ifndef vnl_cost_function_h_
  #define vnl_cost_function_h_
  #ifdef VCL_NEEDS_PRAGMA_INTERFACE
  #pragma interface
  #endif
  //:
  //  \file
  //  \brief Vector->Real function
  //  \author Andrew W. Fitzgibbon, Oxford RRG
  //  \date   23 Oct 97
  //
  // \verbatim
  // Modifications
  //  971023 AWF Initial version.
  //  LSB (Manchester) 26/3/01 Tidied documentation
  //   Feb.2002 - Peter Vanroose - brief doxygen comment placed on single line
  // \endverbatim
  //
  //-----------------------------------------------------------------------------
  
  #include <vnl/vnl_unary_function.h>
  #include <vnl/vnl_vector.h>
  
  //:   An object that represents a function from R^n -> R.
  //    It is commonly used to express the
  //    interface of a minimizer.
  class vnl_cost_function : public vnl_unary_function<double, vnl_vector<double> >
  {
   public:
  
    //! Default constructor
    vnl_cost_function():dim(0) {}
  
    //! Construct with a specified number of unknowns
    vnl_cost_function(int number_of_unknowns):dim(number_of_unknowns) {}
  
    virtual ~vnl_cost_function() {}
  
    //:  The main function.  Given the parameter vector x, compute the value of f(x).
    virtual double f(vnl_vector<double> const& x);
  
    //:  Calculate the gradient of f at parameter vector x.
    virtual void gradf(vnl_vector<double> const& x, vnl_vector<double>& gradient);
  
    //:  Compute one or both of f and g.
    //   Normally implemented in terms of the above two, but may be faster if specialized. f != 0 => compute f
    virtual void compute(vnl_vector<double> const& x, double *f, vnl_vector<double>* g);
  
    //:  Return the number of unknowns
    int get_number_of_unknowns() const { return dim; }
  
    //:  Compute finite-difference gradient
    void fdgradf(vnl_vector<double> const& x, vnl_vector<double>& gradient, double stepsize = 1e-5);
  
    //:  Called when error is printed for user.
    virtual double reported_error(double f_value) { return f_value; }
  
    //:  Conveniences for printing grad, fdgrad
    vnl_vector<double> gradf(vnl_vector<double> const& x);
    vnl_vector<double> fdgradf(vnl_vector<double> const& x);
  
  protected:
  
      //! Set number of unknowns.
      void set_number_of_unknowns(int number_of_unknowns) { dim=number_of_unknowns; }
  
  public:
      int dim;
  };
  
  
  #endif // vnl_cost_function_h_
  