RK4PreciseStep Class Reference

#include <RK4PreciseStep.h>

Public Member Functions
double	distance (const CartesianState &a, const CartesianState &b) const
CartesianState	operator() (const CartesianState &start, const RKCartesianDerivative &deriv, double step, double eps) const
std::pair< CartesianState, double >	stepWithAccuracy (const CartesianState &start, const RKCartesianDerivative &deriv, double step) const

Private Member Functions
bool	verbose () const

Detailed Description

Definition at line 10 of file RK4PreciseStep.h.

Member Function Documentation

double RK4PreciseStep::distance	(	const CartesianState &	a,
		const CartesianState &	b
	)		const

Definition at line 63 of file RK4PreciseStep.cc.

References Basic3DVector< T >::mag(), mag(), CartesianState::momentum(), and CartesianState::position().

Referenced by stepWithAccuracy().

{
    return (a.position() - b.position()).mag() + (a.momentum() - b.momentum()).mag() / b.momentum().mag();
}

CartesianState RK4PreciseStep::operator()	(	const CartesianState &	start,
		const RKCartesianDerivative &	deriv,
		double	step,
		double	eps
	)		const

Definition at line 7 of file RK4PreciseStep.cc.

References gather_cfg::cout, mps_splice::currentStart, SiStripPI::max, min(), Basic3DVector< T >::perp(), CartesianState::position(), funct::pow(), command_line::start, stepWithAccuracy(), verbose(), and Basic3DVector< T >::z().

{
    const double Safety = 0.9;
    double remainigStep = step;
    double stepSize = step;
    CartesianState currentStart = start;
    int nsteps = 0;
    std::pair<CartesianState, double> tryStep;

    do {
    tryStep = stepWithAccuracy( currentStart, deriv, stepSize);
    nsteps++;
    if (tryStep.second <eps) {
        if (remainigStep - stepSize < eps/2) {
        if (verbose()) std::cout << "Accuracy reached, and full step taken in " 
                    << nsteps << " steps" << std::endl;
        return tryStep.first; // we are there
        }
        else {
        remainigStep -= stepSize;
                // increase step size
        double factor =  std::min( Safety * pow( fabs(eps/tryStep.second),0.2), 4.);
        stepSize = std::min( stepSize*factor, remainigStep);
        currentStart = tryStep.first;
        if (verbose()) std::cout << "Accuracy reached, but " << remainigStep 
             << " remain after " << nsteps << " steps. Step size increased by " 
             << factor << " to " << stepSize << std::endl;
        }
    }
    else {
        // decrease step size
        double factor =  std::max( Safety * pow( fabs(eps/tryStep.second),0.25), 0.1);
        stepSize *= factor;
        if (verbose()) std::cout << "Accuracy not yet reached: delta = " << tryStep.second
         << ", step reduced by " << factor << " to " << stepSize 
         << ", (R,z)= " << currentStart.position().perp() 
         << ", " << currentStart.position().z() << std::endl;
    }
    } while (remainigStep > eps/2);

    return tryStep.first;
}

std::pair< CartesianState, double > RK4PreciseStep::stepWithAccuracy	(	const CartesianState &	start,
		const RKCartesianDerivative &	deriv,
		double	step
	)		const

Definition at line 52 of file RK4PreciseStep.cc.

References mps_update::diff, and distance().

Referenced by operator()().

{
    RK4OneStep solver;
    CartesianState one(solver(start, deriv, step));
    CartesianState firstHalf(solver(start, deriv, step/2));
    CartesianState secondHalf(solver(firstHalf, deriv, step/2));
    double diff = distance(one, secondHalf);
    return std::pair<CartesianState, double>(secondHalf,diff);
}

bool RK4PreciseStep::verbose ( ) const

private

Definition at line 68 of file RK4PreciseStep.cc.

Referenced by operator()().

{
  return true;
}