//
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//
//
// $Id$
//
//
// class G4ImplicitEuler
//
// Class description:
//
// Implicit Euler stepper for magnetic field:
//      x_1 = x_0 + h/2 * ( dx(t_0,x_0) + dx(t_0+h,x_0+h*dx(t_0,x_0) ) )
//
// Second order solver.
// Takes the current derivative and add it to the current position.
// Takes the output and its derivative. Adds the mean of both
// derivatives to form the final output.

// W. Wander <wwc@mit.edu> 12/09/97
// -------------------------------------------------------------------

#ifndef G4IMPLICITEULER_HH
#define G4IMPLICITEULER_HH

#include "G4MagErrorStepper.hh"

class G4ImplicitEuler : public G4MagErrorStepper
{

  public:  // with description

    G4ImplicitEuler(G4EquationOfMotion *EqRhs, G4int numberOfVariables = 6) ;
   ~G4ImplicitEuler();

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

  public:  // without description

    G4int IntegratorOrder() const { return 2 ; } ;

  private:

    G4double*  dydxTemp;
    G4double*  yTemp;    
      // Temporaries, created to avoid new/delete on every call
};

#endif /* G4IMPLICITEULER_HH */
