Gabriele Cosmo
158 lines
4.8 KiB
C++
158 lines
4.8 KiB
C++
// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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//
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// G4ModifiedMidpoint implementation
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// Based on modified_midpoint.hpp from boost
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//
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// Author: Dmitry Sorokin - GSoC 2016
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//
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///////////////////////////////////////////////////////////////////////////////
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#include "G4ModifiedMidpoint.hh"
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#include "G4FieldUtils.hh"
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using namespace field_utils;
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G4ModifiedMidpoint::G4ModifiedMidpoint( G4EquationOfMotion* equation,
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G4int nvar, G4int steps )
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: fEquation(equation), fnvar(nvar), fsteps(steps)
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{
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if (nvar <= 0)
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{
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G4Exception("G4ModifiedMidpoint::G4ModifiedMidpoint()",
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"GeomField0002", FatalException,
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"Invalid number of variables; must be greater than zero!");
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}
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}
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void G4ModifiedMidpoint::DoStep( const G4double yIn[], const G4double dydyIn[],
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G4double yOut[], G4double hstep) const
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{
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G4double y0[G4FieldTrack::ncompSVEC];
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G4double y1[G4FieldTrack::ncompSVEC];
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G4double yTemp[G4FieldTrack::ncompSVEC];
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setValue(yIn, Value1D::LabTime, y0, y1, yTemp, yOut);
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G4double dydx[G4FieldTrack::ncompSVEC];
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const G4double h = hstep / fsteps;
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const G4double h2 = 2 * h;
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// y1 = yIn + h * dydx
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for (G4int i = 0; i < fnvar; ++i)
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{
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y1[i] = yIn[i] + h * dydyIn[i];
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}
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fEquation->RightHandSide(y1, dydx);
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copy(y0, yIn);
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// general step
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// yTemp = y1; y1 = y0 + h2 * dydx; y0 = yTemp
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for (G4int i = 1; i < fsteps; ++i)
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{
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copy(yTemp, y1);
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for (G4int j = 0; j < fnvar; ++j)
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{
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y1[j] = y0[j] + h2 * dydx[j];
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}
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copy(y0, yTemp);
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fEquation->RightHandSide(y1, dydx);
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}
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// last step
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// yOut = 0.5 * (y0 + y1 + h * dydx)
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for (G4int i = 0; i < fnvar; ++i)
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{
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yOut[i] = 0.5 * (y0[i] + y1[i] + h * dydx[i]);
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}
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}
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void G4ModifiedMidpoint::DoStep( const G4double yIn[], const G4double dydxIn[],
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G4double yOut[], G4double hstep, G4double yMid[],
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G4double derivs[][G4FieldTrack::ncompSVEC]) const
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{
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G4double y0[G4FieldTrack::ncompSVEC];
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G4double y1[G4FieldTrack::ncompSVEC];
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G4double yTemp[G4FieldTrack::ncompSVEC];
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setValue(yIn, Value1D::LabTime, y0, y1, yTemp, yMid, yOut);
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const G4double h = hstep / fsteps;
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const G4double h2 = 2 * h;
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// y0 = yIn
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copy(y0, yIn);
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// y1 = y0 + h * dydx
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for (G4int i = 0; i < fnvar; ++i)
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{
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y1[i] = y0[i] + h * dydxIn[i];
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}
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// result of first step already gives approximation
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// at the center of the interval
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if(fsteps == 2)
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{
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copy(yMid, y1);
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}
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fEquation->RightHandSide(y1, derivs[0]);
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// general step
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// yTemp = y1; y1 = y0 + h2 * dydx; y0 = yTemp
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for (G4int i = 1; i < fsteps; ++i)
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{
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copy(yTemp, y1);
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for (G4int j = 0; j < fnvar; ++j)
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{
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y1[j] = y0[j] + h2 * derivs[i-1][j];
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}
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copy(y0, yTemp);
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// save approximation at the center of the interval
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if(i == fsteps / 2 - 1 )
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{
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copy(yMid, y1);
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}
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fEquation->RightHandSide(y1, derivs[i]);
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}
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// last step
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// yOut = 0.5 * (y0 + y1 + h * dydx)
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for (G4int i = 0; i < fnvar; ++i)
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{
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yOut[i] = 0.5 * (y0[i] + y1[i] + h * derivs[fsteps-1][i]);
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}
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}
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void G4ModifiedMidpoint::copy(G4double dst[], const G4double src[]) const
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{
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std::memcpy(dst, src, sizeof(G4double) * fnvar);
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}
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