ExpDecayMuon.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 +
//----------------------------------------------------------------------
// Includes
//----------------------------------------------------------------------
#include "MantidCurveFitting/Functions/ExpDecayMuon.h"
#include "MantidAPI/FunctionFactory.h"
#include <cmath>
 
namespace Mantid::CurveFitting::Functions {
 
using namespace CurveFitting;
 
using namespace Kernel;
 
using namespace API;
 
DECLARE_FUNCTION(ExpDecayMuon)
 
void ExpDecayMuon::init() {
  declareParameter("A", 0.2, "Amplitude at time 0");
  declareParameter("Lambda", 0.2, "Decay rate");
}
 
void ExpDecayMuon::function1D(double *out, const double *xValues, const size_t nData) const {
  const double gA0 = getParameter("A");
  const double gs = getParameter("Lambda");
 
  for (size_t i = 0; i < nData; i++) {
    out[i] = gA0 * exp(-gs * (xValues[i]));
  }
}
 
void ExpDecayMuon::functionDeriv1D(Jacobian *out, const double *xValues, const size_t nData) {
  const double gA0 = getParameter("A");
  const double gs = getParameter("Lambda");
 
  for (size_t i = 0; i < nData; i++) {
    double x = xValues[i];
    double e = exp(-gs * x);
    out->set(i, 0, e);            // derivative w.r.t. A (gA0)
    out->set(i, 1, -gA0 * x * e); // derivative w.r.t  Lambda (gs)
  }
}
 
} // namespace Mantid::CurveFitting::Functions