LogNormal.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/LogNormal.h"
#include "MantidAPI/FunctionFactory.h"
#include <cmath>
 
namespace Mantid::CurveFitting::Functions {
 
using namespace CurveFitting;
 
using namespace Kernel;
 
using namespace API;
 
DECLARE_FUNCTION(LogNormal)
 
LogNormal::LogNormal() {
  declareParameter("Height", 1.0, "Overall scaling factor");
  declareParameter("Location", 1.0, "Natural logarithm of the geometric mean");
  declareParameter("Scale", 1.0, "Natural logarithm of the geometric standard deviation");
}
 
void LogNormal::function1D(double *out, const double *xValues, const size_t nData) const {
  const double h = getParameter("Height");
  const double t = getParameter("Location");
  const double b = getParameter("Scale");
 
  for (size_t i = 0; i < nData; i++) {
    double x = xValues[i];
    if (x == 0.0) {
      out[i] = 0.0; // limit of the distribution as x approaches to zero
    } else {
      double c = (log(x) - t) / b;
      out[i] = h / x * exp(-c * c / 2);
    }
  }
}
 
void LogNormal::functionDeriv1D(API::Jacobian *out, const double *xValues, const size_t nData) {
  const double h = getParameter("Height");
  const double t = getParameter("Location");
  const double b = getParameter("Scale");
 
  for (size_t i = 0; i < nData; i++) {
    double x = xValues[i];
    if (x == 0.0) {
      out->set(i, 0,
               0.0); // all partial derivatives approach to 0 as x goes to 0
      out->set(i, 1, 0.0);
      out->set(i, 2, 0.0);
    } else {
      double c = (log(x) - t) / b;
      double e = exp(-c * c / 2) / x;
      out->set(i, 0, e); // partial derivative with respect to Height
      out->set(i, 1,
               h * e * (c / b)); // partial derivative with respect to Location parameter
      out->set(i, 2,
               h * e * (c * c / b)); // partial derivative with respect to Scale parameter
    }
  }
}
 
} // namespace Mantid::CurveFitting::Functions