text: #ifndef MN_GradientCalculator_H_
  #define MN_GradientCalculator_H_
  
  class MinimumParameters;
  class FunctionGradient;
  
  class GradientCalculator {
  
  public:
    
    virtual ~GradientCalculator() {}
  
    virtual FunctionGradient operator()(const MinimumParameters&) const = 0;
  
    virtual FunctionGradient operator()(const MinimumParameters&,
  				      const FunctionGradient&) const = 0;
  };
  
  #endif //MN_GradientCalculator_H_
  