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//
// G4SimpleRunge
//
// Class description:
//
// Simple Runge:
//
//        x_1 = x_0 + h * ( dx( t_0+h/2, x_0 + h/2 * dx( t_0, x_0) ) )
//
// Second order solver.
// Takes the derivative at a position to be assumed at the middle of the
// Step and adds it to the current position.

// Created: W.Wander <wwc@mit.edu>, 12/09/1997
// -------------------------------------------------------------------
#ifndef G4SIMPLERUNGE_HH
#define G4SIMPLERUNGE_HH

#include "G4MagErrorStepper.hh"

class G4SimpleRunge : public G4MagErrorStepper
{

  public:  // with description

    G4SimpleRunge(G4EquationOfMotion* EquationRhs, G4int numberOfVariables = 6) ;
   ~G4SimpleRunge();
      // Constructor and destructor.

    void DumbStepper( const G4double y[],
                      const G4double dydx[],
                            G4double h,
                            G4double yout[] );

  public:  // without description
  
    inline G4int IntegratorOrder() const { return 2; }

  private:

    G4int fNumberOfVariables = 0;

    G4double* dydxTemp = nullptr;
    G4double* yTemp = nullptr;
      // scratch space    
};

#endif
