TimeAtSampleStrategyIndirect.cpp

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// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2018 ISIS Rutherford Appleton Laboratory UKRI,
//   NScD Oak Ridge National Laboratory, European Spallation Source,
//   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
// SPDX - License - Identifier: GPL - 3.0 +
#include "MantidAlgorithms/TimeAtSampleStrategyIndirect.h"
#include "MantidAPI/MatrixWorkspace.h"
#include "MantidAPI/SpectrumInfo.h"
#include "MantidGeometry/IComponent.h"
#include "MantidGeometry/IDetector.h"
#include "MantidGeometry/Instrument.h"
#include "MantidGeometry/Instrument/ParameterMap.h"
#include "MantidGeometry/Instrument/ReferenceFrame.h"
#include "MantidKernel/Logger.h"
#include "MantidKernel/PhysicalConstants.h"
#include "MantidKernel/V3D.h"
#include <cmath>
#include <memory>
#include <sstream>
#include <utility>
 
using namespace Mantid::Kernel;
using namespace Mantid::Geometry;
using namespace Mantid::API;
 
namespace Mantid::Algorithms {
 
TimeAtSampleStrategyIndirect::TimeAtSampleStrategyIndirect(MatrixWorkspace_const_sptr ws)
    : m_ws(std::move(ws)), m_spectrumInfo(m_ws->spectrumInfo()) {}
 
Correction TimeAtSampleStrategyIndirect::calculate(const size_t &workspace_index) const {
 
  // A constant among all spectra
  constexpr double TWO_MEV_OVER_MASS = 2. * PhysicalConstants::meV / PhysicalConstants::NeutronMass;
 
  const IDetector *det = &m_spectrumInfo.detector(workspace_index);
  if (m_spectrumInfo.isMonitor(workspace_index)) {
    // use the same math as TimeAtSampleStrategyElastic
    const double L1s = m_spectrumInfo.l1();
    const auto &beamDir = m_ws->getInstrument()->getReferenceFrame()->vecPointingAlongBeam();
    const double L1m = beamDir.scalar_prod(m_spectrumInfo.sourcePosition() - m_spectrumInfo.position(workspace_index));
    const double scale = std::abs(L1s / L1m);
    return Correction(0., scale);
  }
 
  // Get E_fix
  double efix{0.};
  try {
    // Get the parameter map
    const ParameterMap &pmap = m_ws->constInstrumentParameters();
    Parameter_sptr par = pmap.getRecursive(det, "Efixed");
    if (par) {
      efix = par->value<double>();
    }
  } catch (std::runtime_error &) {
    // Throws if a DetectorGroup, use single provided value
    std::stringstream errmsg;
    errmsg << "Inelastic instrument detector " << det->getID() << " of spectrum " << workspace_index
           << " does not have EFixed ";
    throw std::runtime_error(errmsg.str());
  }
  if (efix <= 0.) {
    std::stringstream errmsg;
    errmsg << "Inelastic instrument detector " << det->getID() << " of spectrum " << workspace_index
           << " does not have EFixed ";
    throw std::runtime_error(errmsg.str());
  }
 
  const double l2 = m_spectrumInfo.l2(workspace_index);
  const double shift = -1. * l2 / sqrt(efix * TWO_MEV_OVER_MASS);
 
  // 1.0 * tof + shift
  return Correction(shift, 1.0);
}
 
} // namespace Mantid::Algorithms