TGeoMaterialInterface.cc

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/* Copyright 2008-2014, Technische Universitaet Muenchen,
   Authors: Christian Hoeppner & Sebastian Neubert & Johannes Rauch

   This file is part of GENFIT.

   GENFIT is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as published
   by the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   GENFIT is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with GENFIT.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "TGeoMaterialInterface.h"
#include "Exception.h"
#include "IO.h"

#include <TGeoMedium.h>
#include <TGeoMaterial.h>
#include <TGeoManager.h>
#include <assert.h>
#include <math.h>


namespace genfit {

double MeanExcEnergy_get(int Z);
double MeanExcEnergy_get(TGeoMaterial*);


bool
TGeoMaterialInterface::initTrack(double posX, double posY, double posZ,
                                   double dirX, double dirY, double dirZ){
  #ifdef DEBUG
  debugOut << "TGeoMaterialInterface::initTrack. \n";
  debugOut << "Pos    "; TVector3(posX, posY, posZ).Print();
  debugOut << "Dir    "; TVector3(dirX, dirY, dirZ).Print();
  #endif

  // Move to the new point.
  bool result = !gGeoManager->IsSameLocation(posX, posY, posZ, kTRUE);
  // Set the intended direction.
  gGeoManager->SetCurrentDirection(dirX, dirY, dirZ);

  if (debugLvl_ > 0) {
    debugOut << "      TGeoMaterialInterface::initTrack at \n";
    debugOut << "      position:  "; TVector3(posX, posY, posZ).Print();
    debugOut << "      direction: "; TVector3(dirX, dirY, dirZ).Print();
  }

  return result;
}


Material TGeoMaterialInterface::getMaterialParameters() {

  TGeoMaterial* mat = gGeoManager->GetCurrentVolume()->GetMedium()->GetMaterial();
  return Material(mat->GetDensity(), mat->GetZ(), mat->GetA(), mat->GetRadLen(), MeanExcEnergy_get(mat));

}


double
TGeoMaterialInterface::findNextBoundary(const RKTrackRep* rep,
                                          const M1x7& stateOrig,
                                          double sMax, // signed
                                          bool varField)
{
  const double delta(1.E-2); // cm, distance limit beneath which straight-line steps are taken.
  const double epsilon(1.E-1); // cm, allowed upper bound on arch
  // deviation from straight line

  M1x3 SA;
  M1x7 state7, oldState7;
  oldState7 = stateOrig;

  int stepSign(sMax < 0 ? -1 : 1);

  double s = 0;  // trajectory length to boundary

  const unsigned maxIt = 300;
  unsigned it = 0;

  // Initialize the geometry to the current location (set by caller).
  gGeoManager->FindNextBoundary(fabs(sMax) - s);
  double safety = gGeoManager->GetSafeDistance(); // >= 0
  double slDist = gGeoManager->GetStep();

  // this should not happen, but it happens sometimes.
  // The reason are probably overlaps in the geometry.
  // Without this "hack" many small steps with size of minStep will be made,
  // until eventually the maximum number of iterations are exceeded and the extrapolation fails
  if (slDist < safety) 
    slDist = safety;
  double step = slDist;

  if (debugLvl_ > 0)
    debugOut << "   safety = " << safety << "; step, slDist = " << step << "\n";

  while (1) {
    if (++it > maxIt){
      Exception exc("TGeoMaterialInterface::findNextBoundary ==> maximum number of iterations exceeded",__LINE__,__FILE__);
      exc.setFatal();
      throw exc;
    }

    // No boundary in sight?
    if (s + safety > fabs(sMax)) {
      if (debugLvl_ > 0)
        debugOut << "   next boundary is further away than sMax \n";
      return stepSign*(s + safety); //sMax;
    }

    // Are we at the boundary?
    if (slDist < delta) {
      if (debugLvl_ > 0)
        debugOut << "   very close to the boundary -> return"
        << " stepSign*(s + slDist) = "
        << stepSign << "*(" << s + slDist << ")\n";
      return stepSign*(s + slDist);
    }

    // We have to find whether there's any boundary on our path.

    // Follow curved arch, then see if we may have missed a boundary.
    // Always propagate complete way from original start to avoid
    // inconsistent extrapolations.
    state7 = stateOrig;
    rep->RKPropagate(state7, nullptr, SA, stepSign*(s + step), varField);

    // Straight line distance² between extrapolation finish and
    // the end of the previously determined safe segment.
    double dist2 = (pow(state7[0] - oldState7[0], 2)
        + pow(state7[1] - oldState7[1], 2)
        + pow(state7[2] - oldState7[2], 2));
    // Maximal lateral deviation².
    double maxDeviation2 = 0.25*(step*step - dist2);

    if (step > safety
        && maxDeviation2 > epsilon*epsilon) {
      // Need to take a shorter step to reliably estimate material,
      // but only if we didn't move by safety.  In order to avoid
      // issues with roundoff we check 'step > safety' instead of
      // 'step != safety'.  If we moved by safety, there couldn't have
      // been a boundary that we missed along the path, but we could
      // be on the boundary.

      // Take a shorter step, but never shorter than safety.
      step = std::max(step / 2, safety);
    } else {
      gGeoManager->PushPoint();
      bool volChanged = initTrack(state7[0], state7[1], state7[2],
          stepSign*state7[3], stepSign*state7[4],
          stepSign*state7[5]);

      if (volChanged) {
        if (debugLvl_ > 0)
          debugOut << "   volChanged\n";
        // Move back to start.
        gGeoManager->PopPoint();

        // Extrapolation may not take the exact step length we asked
        // for, so it can happen that a requested step < safety takes
        // us across the boundary.  This is then the best estimate we
        // can get of the distance to the boundary with the stepper.
        if (step <= safety) {
          if (debugLvl_ > 0)
            debugOut << "   step <= safety, return stepSign*(s + step) = " << stepSign*(s + step) << "\n";
          return stepSign*(s + step);
        }

        // Volume changed during the extrapolation.  Take a shorter
        // step, but never shorter than safety.
        step = std::max(step / 2, safety);
      } else {
        // we're in the new place, the step was safe, advance
        s += step;

        oldState7 = state7;
        gGeoManager->PopDummy();  // Pop stack, but stay in place.

        gGeoManager->FindNextBoundary(fabs(sMax) - s);
        safety = gGeoManager->GetSafeDistance();
        slDist = gGeoManager->GetStep();

        // this should not happen, but it happens sometimes.
        // The reason are probably overlaps in the geometry.
        // Without this "hack" many small steps with size of minStep will be made,
        // until eventually the maximum number of iterations are exceeded and the extrapolation fails
        if (slDist < safety)
          slDist = safety;
        step = slDist;
        if (debugLvl_ > 0)
          debugOut << "   safety = " << safety << "; step, slDist = " << step << "\n";
      }
    }
  }
}


/*
Reference for elemental mean excitation energies at:
http://physics.nist.gov/PhysRefData/XrayMassCoef/tab1.html

Code ported from GEANT 3
*/

const int MeanExcEnergy_NELEMENTS = 93; // 0 = vacuum, 1 = hydrogen, 92 = uranium
const double MeanExcEnergy_vals[MeanExcEnergy_NELEMENTS] = {
  1.e15, 19.2, 41.8, 40.0, 63.7, 76.0, 78., 82.0,
  95.0, 115.0, 137.0, 149.0, 156.0, 166.0, 173.0, 173.0,
  180.0, 174.0, 188.0, 190.0, 191.0, 216.0, 233.0, 245.0,
  257.0, 272.0, 286.0, 297.0, 311.0, 322.0, 330.0, 334.0,
  350.0, 347.0, 348.0, 343.0, 352.0, 363.0, 366.0, 379.0,
  393.0, 417.0, 424.0, 428.0, 441.0, 449.0, 470.0, 470.0,
  469.0, 488.0, 488.0, 487.0, 485.0, 491.0, 482.0, 488.0,
  491.0, 501.0, 523.0, 535.0, 546.0, 560.0, 574.0, 580.0,
  591.0, 614.0, 628.0, 650.0, 658.0, 674.0, 684.0, 694.0,
  705.0, 718.0, 727.0, 736.0, 746.0, 757.0, 790.0, 790.0,
  800.0, 810.0, 823.0, 823.0, 830.0, 825.0, 794.0, 827.0,
  826.0, 841.0, 847.0, 878.0, 890.0, };
// Logarithms of the previous table, used to calculate mixtures.
const double MeanExcEnergy_logs[MeanExcEnergy_NELEMENTS] = {
  34.5388, 2.95491, 3.7329, 3.68888, 4.15418, 4.33073, 4.35671, 4.40672, 
  4.55388, 4.74493, 4.91998, 5.00395, 5.04986, 5.11199, 5.15329, 5.15329, 
  5.19296, 5.15906, 5.23644, 5.24702, 5.25227, 5.37528, 5.45104, 5.50126, 
  5.54908, 5.6058, 5.65599, 5.69373, 5.73979, 5.77455, 5.79909, 5.81114, 
  5.85793, 5.84932, 5.8522, 5.83773, 5.86363, 5.8944, 5.90263, 5.93754, 
  5.97381, 6.03309, 6.04973, 6.05912, 6.08904, 6.10702, 6.15273, 6.15273, 
  6.1506, 6.19032, 6.19032, 6.18826, 6.18415, 6.19644, 6.17794, 6.19032, 
  6.19644, 6.21661, 6.25958, 6.28227, 6.30262, 6.32794, 6.35263, 6.36303, 
  6.38182, 6.41999, 6.44254, 6.47697, 6.4892, 6.51323, 6.52796, 6.54247, 
  6.5582, 6.57647, 6.58893, 6.60123, 6.61473, 6.62936, 6.67203, 6.67203, 
  6.68461, 6.69703, 6.71296, 6.71296, 6.72143, 6.71538, 6.67708, 6.7178, 
  6.71659, 6.73459, 6.7417, 6.77765, 6.79122, };


double
MeanExcEnergy_get(int Z, bool logs = false) {
  assert(Z >= 0 && Z < MeanExcEnergy_NELEMENTS);
  if (logs)
    return MeanExcEnergy_logs[Z];
  else
    return MeanExcEnergy_vals[Z];
}


double
MeanExcEnergy_get(TGeoMaterial* mat) {
  if (mat->IsMixture()) {
    // The mean excitation energy is calculated as the geometric mean
    // of the mEEs of the components, weighted for abundance.
    double logMEE = 0.;
    double denom  = 0.;
    TGeoMixture* mix = (TGeoMixture*)mat;
    for (int i = 0; i < mix->GetNelements(); ++i) {
      int index = int(mix->GetZmixt()[i]);
      double weight = mix->GetWmixt()[i] * mix->GetZmixt()[i] / mix->GetAmixt()[i];
      logMEE += weight * MeanExcEnergy_get(index, true);
      denom  += weight;
    }
    logMEE /= denom;
    return exp(logMEE);
  } 

  // not a mixture
  int index = int(mat->GetZ());
  return MeanExcEnergy_get(index, false);
}


} /* End of namespace genfit */