Bk2BkExpConvPV.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 <cmath>
 
#include "MantidAPI/Axis.h"
#include "MantidAPI/FunctionFactory.h"
#include "MantidAPI/MatrixWorkspace.h"
#include "MantidCurveFitting/Functions/Bk2BkExpConvPV.h"
#include "MantidCurveFitting/SpecialFunctionSupport.h"
#include "MantidKernel/System.h"
#include "MantidKernel/UnitFactory.h"
 
#include <gsl/gsl_sf_erf.h>
#include <gsl/gsl_sf_lambert.h>
 
using namespace Mantid::Kernel;
 
using namespace Mantid::API;
 
namespace Mantid::CurveFitting::Functions {
 
using namespace CurveFitting;
using namespace CurveFitting::SpecialFunctionSupport;
namespace {
Kernel::Logger g_log("Bk2BkExpConvPV");
} // namespace
 
DECLARE_FUNCTION(Bk2BkExpConvPV)
 
 
void Bk2BkExpConvPV::init() {
  declareParameter("X0", -0.0, "Location of the peak");
  declareParameter("Intensity", 0.0, "Integrated intensity");
  declareParameter("Alpha", 0.04, "Exponential rise");
  declareParameter("Beta", 0.02, "Exponential decay");
  declareParameter("Sigma2", 1.0, "Sigma squared");
  declareParameter("Gamma", 0.0);
}
 
void Bk2BkExpConvPV::setHeight(const double h) {
  setParameter("Intensity", 1);
  double h0 = height();
 
  // avoid divide by zero
  double minCutOff = 100.0 * std::numeric_limits<double>::min();
  if (h0 >= 0 && h0 < minCutOff)
    h0 = minCutOff;
  else if (h0 < 0 && h0 > -minCutOff)
    h0 = -minCutOff;
 
  setParameter("Intensity", h / h0);
}
 
double Bk2BkExpConvPV::height() const {
  double height[1];
  double peakCentre[1];
  peakCentre[0] = this->getParameter("X0");
  this->functionLocal(height, peakCentre, 1);
  return height[0];
}
 
double Bk2BkExpConvPV::fwhm() const {
  // get sigma of Gauss with same FWHM as voigt (H)
  double H, eta;
  calHandEta(getParameter("Sigma2"), getParameter("Gamma"), H, eta);
  const auto s = H / (2 * sqrt(2 * M_LN2)); // FWHM = 2*sqrt(2*ln(2))*sigma
  const auto w0 = expWidth();
  // Gaussian and B2B exp widths don't add in quadrature. The following
  // tends to gaussian at large S and at S=0 is equal to the intrinsic width of
  // the B2B exp (good to <3% for typical params)
  // (same Eq. used in BackToBackExponential)
  return w0 * exp(-0.5 * M_LN2 * s / w0) + 2 * sqrt(2 * M_LN2) * s;
}
 
void Bk2BkExpConvPV::setFwhm(const double w) {
  const auto h0 = height();
  const auto w0 = expWidth();
  if (w > w0) {
    const auto a = 0.5 * M_LN2;
    const auto b = 2 * sqrt(2 * M_LN2);
    // Can calculate FWHM of voigt (from FWHM of Gauss componeont from Eq. in BackToBackExponential)
    // From Eq. in calHandEta assuming FWHM of Gauss and Lorz are equal fwhm_pv = 1.6364*fwhm_gauss
    const auto fwhm_gauss =
        b * w0 * (gsl_sf_lambert_W0(-(a / b) * exp(-(a / b) * (w / w0))) / a + (w / w0) / b) / 1.6364;
    setParameter("Sigma2", std::pow(fwhm_gauss / b, 2));
    setParameter("Gamma", fwhm_gauss / 2);
  } else {
    // set to some small number relative to w0
    setParameter("Sigma2", 1e-6);
    setParameter("Gamma", 1e-6);
  }
  setHeight(h0);
}
 
void Bk2BkExpConvPV::setCentre(const double c) { setParameter("X0", c); }
 
double Bk2BkExpConvPV::centre() const { return getParameter("X0"); }
 
void Bk2BkExpConvPV::setMatrixWorkspace(std::shared_ptr<const API::MatrixWorkspace> workspace, size_t wi, double startX,
                                        double endX) {
  IFunctionMW::setMatrixWorkspace(workspace, wi, startX, endX);
}
 
void Bk2BkExpConvPV::functionLocal(double *out, const double *xValues, const size_t nData) const {
  // 1. Prepare constants
  const double alpha = this->getParameter("Alpha");
  const double beta = this->getParameter("Beta");
  const double sigma2 = this->getParameter("Sigma2");
  const double gamma = this->getParameter("Gamma");
  const double intensity = this->getParameter("Intensity");
  const double x0 = this->getParameter("X0");
 
  double invert_sqrt2sigma = 1.0 / sqrt(2.0 * sigma2);
  double N = alpha * beta * 0.5 / (alpha + beta);
 
  double H, eta;
  calHandEta(sigma2, gamma, H, eta);
 
  g_log.debug() << "DB1143:  nData = " << nData << " From " << xValues[0] << " To " << xValues[nData - 1]
                << " X0 = " << x0 << " Intensity = " << intensity << " alpha = " << alpha << " beta = " << beta
                << " H = " << H << " eta = " << eta << '\n';
 
  // 2. Do calculation for each data point within extent of peak (avoid NaNs)
  double extent = 10 * fwhm();
  for (size_t id = 0; id < nData; ++id) {
    double dT = xValues[id] - x0;
    if (fabs(dT) < extent) {
      double omega = calOmega(dT, eta, N, alpha, beta, H, sigma2, invert_sqrt2sigma);
      out[id] = intensity * omega;
    } else {
      out[id] = 0.0;
    }
  }
}
 
void Bk2BkExpConvPV::functionDerivLocal(API::Jacobian * /*jacobian*/, const double * /*xValues*/,
                                        const size_t /*nData*/) {
  throw Mantid::Kernel::Exception::NotImplementedError("functionDerivLocal is not implemented for Bk2BkExpConvPV.");
}
 
void Bk2BkExpConvPV::functionDeriv(const API::FunctionDomain &domain, API::Jacobian &jacobian) {
  calNumericalDeriv(domain, jacobian);
}
 
double Bk2BkExpConvPV::calOmega(double x, double eta, double N, double alpha, double beta, double H, double sigma2,
                                double invert_sqrt2sigma) const {
  // 1. Prepare
  std::complex<double> p(alpha * x, alpha * H * 0.5);
  std::complex<double> q(-beta * x, beta * H * 0.5);
 
  double u = 0.5 * alpha * (alpha * sigma2 + 2 * x);
  double y = (alpha * sigma2 + x) * invert_sqrt2sigma;
 
  double v = 0.5 * beta * (beta * sigma2 - 2 * x);
  double z = (beta * sigma2 - x) * invert_sqrt2sigma;
 
  // 2. Calculate
  double omega1 = (1 - eta) * N * (exp(u + gsl_sf_log_erfc(y)) + exp(v + gsl_sf_log_erfc(z)));
  double omega2;
  if (eta < 1.0E-8) {
    omega2 = 0.0;
  } else {
    omega2 = 2 * N * eta / M_PI * (imag(exponentialIntegral(p)) + imag(exponentialIntegral(q)));
  }
  double omega = omega1 - omega2;
 
  return omega;
}
 
void Bk2BkExpConvPV::geneatePeak(double *out, const double *xValues, const size_t nData) {
  this->functionLocal(out, xValues, nData);
}
 
void Bk2BkExpConvPV::calHandEta(double sigma2, double gamma, double &H, double &eta) const {
  // 1. Calculate H
  double H_G = sqrt(8.0 * sigma2 * M_LN2); // FWHM Gauss
  double H_L = 2 * gamma;                  // FWHM lorz
 
  double temp1 = std::pow(H_L, 5) + 0.07842 * H_G * std::pow(H_L, 4) + 4.47163 * std::pow(H_G, 2) * std::pow(H_L, 3) +
                 2.42843 * std::pow(H_G, 3) * std::pow(H_L, 2) + 2.69269 * std::pow(H_G, 4) * H_L + std::pow(H_G, 5);
 
  H = std::pow(temp1, 0.2); // FWHM of PV
 
  // 2. Calculate eta
  double gam_pv = H_L / H;
  eta = 1.36603 * gam_pv - 0.47719 * std::pow(gam_pv, 2) + 0.11116 * std::pow(gam_pv, 3);
 
  if (eta > 1 || eta < 0) {
    g_log.error() << "Bk2BkExpConvPV: Calculated eta = " << eta << " is out of range [0, 1].\n";
  }
}
 
double Bk2BkExpConvPV::expWidth() const {
  const double a = getParameter("Alpha");
  const double b = getParameter("Beta");
  return M_LN2 * (a + b) / (a * b);
}
 
} // namespace Mantid::CurveFitting::Functions