Gabriele Cosmo
165 lines
4.6 KiB
C++
165 lines
4.6 KiB
C++
// This code implementation is the intellectual property of
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// the GEANT4 collaboration.
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//
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// By copying, distributing or modifying the Program (or any work
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// based on the Program) you indicate your acceptance of this statement,
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// and all its terms.
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//
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// $Id: G4ClassicalRK4.cc,v 1.3 2000/11/01 15:15:52 gcosmo Exp $
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// GEANT4 tag $Name: geant4-03-01 $
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//
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#include "G4ClassicalRK4.hh"
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#include "G4ThreeVector.hh"
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//////////////////////////////////////////////////////////////////
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//
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// Constructor sets the number of variables (default = 6)
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G4ClassicalRK4::G4ClassicalRK4(G4Mag_EqRhs *EqRhs, G4int numberOfVariables)
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: G4MagErrorStepper(EqRhs, numberOfVariables),
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fNumberOfVariables(numberOfVariables)
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{
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dydxm = new G4double[fNumberOfVariables];
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dydxt = new G4double[fNumberOfVariables];
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yt = new G4double[fNumberOfVariables];
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}
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////////////////////////////////////////////////////////////////
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//
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// Destructor
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G4ClassicalRK4::~G4ClassicalRK4()
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{
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delete[] dydxm;
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delete[] dydxt;
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delete[] yt;
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}
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//////////////////////////////////////////////////////////////////////
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//
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// Given values for the variables y[0,..,n-1] and their derivatives
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// dydx[0,...,n-1] known at x, use the classical 4th Runge-Kutta
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// method to advance the solution over an interval h and return the
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// incremented variables as yout[0,...,n-1], which not be a distinct
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// array from y. The user supplies the routine RightHandSide(x,y,dydx),
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// which returns derivatives dydx at x. The source is routine rk4 from
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// NRC p. 712-713 .
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void
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G4ClassicalRK4::DumbStepper( const G4double yIn[],
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const G4double dydx[],
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G4double h,
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G4double yOut[])
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{
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const G4int nvar = fNumberOfVariables; // GetNumberOfVariables();
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G4int i;
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G4double hh = h*0.5 , h6 = h/6.0 ;
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for(i=0;i<nvar;i++)
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{
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yt[i] = yIn[i] + hh*dydx[i] ; // 1st Step K1=h*dydx
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}
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RightHandSide(yt,dydxt) ; // 2nd Step K2=h*dydxt
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for(i=0;i<nvar;i++)
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{
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yt[i] = yIn[i] + hh*dydxt[i] ;
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}
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RightHandSide(yt,dydxm) ; // 3rd Step K3=h*dydxm
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for(i=0;i<nvar;i++)
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{
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yt[i] = yIn[i] + h*dydxm[i] ;
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dydxm[i] += dydxt[i] ; // now dydxm=(K2+K3)/h
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}
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RightHandSide(yt,dydxt) ; // 4th Step K4=h*dydxt
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for(i=0;i<nvar;i++) // Final RK4 output
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{
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yOut[i] = yIn[i] + h6*(dydx[i]+dydxt[i]+2.0*dydxm[i]); //+K1/6+K4/6+(K2+K3)/3
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}
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// NormaliseTangentVector( yOut );
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return ;
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} // end of DumbStepper ....................................................
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////////////////////////////////////////////////////////////////////
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//
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//
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void
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G4ClassicalRK4::StepWithEst( const G4double yIn[],
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const G4double dydx[],
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G4double h,
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G4double yOut[],
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G4double& alpha2,
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G4double& beta2,
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const G4double B1[],
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G4double B2[] )
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{
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G4Exception(" G4ClassicalRK4::StepWithEst ERROR: this Method is no longer used.");
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#if 0 // const G4int nvar = 6 ;
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G4int nvar = GetNumberOfVariables();
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G4int i;
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G4double hh = h*0.5 , h6 = h/6.0 ;
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G4double B[3] ;
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alpha2 = 0 ;
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beta2 = 0 ;
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for(i=0;i<nvar;i++)
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{
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yt[i] = yIn[i] + hh*dydx[i] ; // 1st Step K1=h*dydx
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}
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GetEquationOfMotion()->EvaluateRhsReturnB(yt,dydxt,B) ; // Calculates yderive &
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// returns B too!
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// RightHandSide(yt,dydxt) ; // 2nd Step K2=h*dydxt
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for(i=0;i<nvar;i++)
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{
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yt[i] = yIn[i] + hh*dydxt[i] ;
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}
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GetEquationOfMotion()->EvaluateRhsReturnB(yt,dydxm,B2) ;
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// RightHandSide(yt,dydxm) ; // 3rd Step K3=h*dydxm
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for(i=0;i<3;i++)
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{
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beta2 += dydx[i+3] *dydx[i+3]
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+ dydxt[i+3]*dydxt[i+3]
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+ dydxm[i+3]*dydxm[i+3] ;
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alpha2 += B1[i]*B1[i] + B[i]*B[i] + B2[i]*B2[i] ;
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}
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for(i=0;i<nvar;i++)
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{
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yt[i] = yIn[i] + h*dydxm[i] ;
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dydxm[i] += dydxt[i] ; // now dydxm=(K2+K3)/h
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}
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GetEquationOfMotion()->EvaluateRhsReturnB(yt,dydxt,B2) ;
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// RightHandSide(yt,dydxt) ; // 4th Step K4=h*dydxt
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for(i=0;i<nvar;i++) // Final RK4 output
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{
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yOut[i] = yIn[i] + h6*(dydx[i]+dydxt[i]+2.0*dydxm[i]); //+K1/6+K4/6+(K2+K3)/3
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}
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for(i=0;i<3;i++)
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{
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beta2 += dydxt[i+3]*dydxt[i+3] ;
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alpha2 += B2[i]*B2[i] ;
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}
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beta2 *= 0.25*h*h;
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alpha2 *= sqr(GetEquationOfMotion()->FCof()*h)*0.25 ;
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// NormaliseTangentVector( yOut );
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#endif
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return ;
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} // end of StepWithEst ......................................................
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