StaticKuboToyabeTimesExpDecay.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 "MantidCurveFitting/Functions/StaticKuboToyabeTimesExpDecay.h"
#include "MantidAPI/FunctionFactory.h"
#include <cmath>
 
namespace Mantid::CurveFitting::Functions {
 
using namespace CurveFitting;
 
using namespace Kernel;
 
using namespace API;
 
DECLARE_FUNCTION(StaticKuboToyabeTimesExpDecay)
 
void StaticKuboToyabeTimesExpDecay::init() {
  declareParameter("A", 0.2, "Amplitude at time 0");
  declareParameter("Delta", 0.2, "StaticKuboToyabe decay rate");
  declareParameter("Lambda", 0.2, "Exponential decay rate");
}
 
void StaticKuboToyabeTimesExpDecay::function1D(double *out, const double *xValues, const size_t nData) const {
  const double A = getParameter("A");
  const double D = getParameter("Delta");
  const double L = getParameter("Lambda");
 
  const double C1 = 2.0 / 3;
  const double C2 = 1.0 / 3;
 
  for (size_t i = 0; i < nData; i++) {
    double x = xValues[i];
    double DXSquared = pow(D * x, 2);
    out[i] = A * (exp(-DXSquared / 2) * (1 - DXSquared) * C1 + C2) * exp(-L * x);
  }
}
 
} // namespace Mantid::CurveFitting::Functions