BackToBackExponential.h

// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2007 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 +
#pragma once

//----------------------------------------------------------------------
// Includes
//----------------------------------------------------------------------
#include "MantidAPI/IPeakFunction.h"
#include "MantidCurveFitting/DllConfig.h"

namespace Mantid {
namespace CurveFitting {
namespace Functions {
/**
Provide BackToBackExponential peak shape function interface to IPeakFunction.
That is the function:

  I*(A*B/(A+B)/2)*(exp(A/2*(A*S^2+2*(x-X0)))*erfc((A*S^2+(x-X0))/sqrt(2*S^2))+exp(B/2*(B*S^2-2*(x-X0)))*erfc((B*S^2-(x-X0))/sqrt(2*S^2))).

Function parameters:
<UL>
<LI> I - Integrated intensity of peak (default 0.0)</LI>
<LI> A - exponential constant of rising part of neutron pulse (default 1.0)</LI>
<LI> B - exponential constant of decaying part of neutron pulse (default
0.05)</LI>
<LI> X0 - peak position (default 0.0)</LI>
<LI> S - standard deviation of gaussian part of peakshape function (default
1.0)</LI>
</UL>

@author Anders Markvardsen, ISIS, RAL
@date 9/11/2009
*/
class MANTID_CURVEFITTING_DLL BackToBackExponential : public API::IPeakFunction {
public:
  /// Default constructor.
  BackToBackExponential() : API::IPeakFunction() {}

  /// overwrite IPeakFunction base class methods
  double centre() const override { return getParameter("X0"); }
  void setCentre(const double c) override { setParameter("X0", c); }
  double height() const override;
  void setHeight(const double h) override;
  double fwhm() const override;
  void setFwhm(const double w) override;
  double intensity() const override { return getParameter("I"); }
  double intensityError() const override { return getError("I"); }
  void setIntensity(const double newIntensity) override { setParameter("I", newIntensity); }
  std::string getWidthParameterName() const override { return "S"; }

  /// overwrite IFunction base class methods
  std::string name() const override { return "BackToBackExponential"; }
  const std::string category() const override { return "Peak"; }
  void function1D(double *out, const double *xValues, const size_t nData) const override;
  void functionDeriv1D(API::Jacobian *jacobian, const double *xValues, const size_t nData) override;

protected:
  /// overwrite IFunction base class method, which declare function parameters
  void init() override;
  /// Function evaluation method to be implemented in the inherited classes
  void functionLocal(double *, const double *, const size_t) const override {}
  /// Derivative evaluation method to be implemented in the inherited classes
  void functionDerivLocal(API::Jacobian *, const double *, const size_t) override {}
  double expWidth() const;
};

using BackToBackExponential_sptr = std::shared_ptr<BackToBackExponential>;

} // namespace Functions
} // namespace CurveFitting
} // namespace Mantid