GModelSpectralSuperExpPlaw.cpp

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/***************************************************************************
 *   GModelSpectralSuperExpPlaw.cpp - Super exp. cut off power law model   *
 * ----------------------------------------------------------------------- *
 *  copyright (C) 2014-2021 by Michael Mayer                               *
 * ----------------------------------------------------------------------- *
 *                                                                         *
 *  This program is free software: you can redistribute it and/or modify   *
 *  it under the terms of the GNU General Public License as published by   *
 *  the Free Software Foundation, either version 3 of the License, or      *
 *  (at your option) any later version.                                    *
 *                                                                         *
 *  This program is distributed in the hope that it will be useful,        *
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of         *
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the          *
 *  GNU General Public License for more details.                           *
 *                                                                         *
 *  You should have received a copy of the GNU General Public License      *
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.  *
 *                                                                         *
 ***************************************************************************/
/**
 * @file GModelSpectralSuperExpPlaw.cpp
 * @brief Super exponential cut off power law spectral class implementation
 * @author Michael Mayer
 */
 
/* __ Includes ___________________________________________________________ */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <cmath>
#include "GException.hpp"
#include "GTools.hpp"
#include "GRan.hpp"
#include "GIntegral.hpp"
#include "GModelSpectralSuperExpPlaw.hpp"
#include "GModelSpectralRegistry.hpp"
 
/* __ Constants __________________________________________________________ */
 
/* __ Globals ____________________________________________________________ */
const GModelSpectralSuperExpPlaw g_spectral_seplaw_seed1("SuperExponentialCutoffPowerLaw",
                                                         "Prefactor",
                                                         "Index1",
                                                         "PivotEnergy",
                                                         "CutoffEnergy",
                                                         "Index2");
const GModelSpectralRegistry     g_spectral_seplaw_registry1(&g_spectral_seplaw_seed1);
#if defined(G_LEGACY_XML_FORMAT)
const GModelSpectralSuperExpPlaw g_spectral_seplaw_seed2("PLSuperExpCutoff",
                                                         "Prefactor",
                                                         "Index1",
                                                         "Scale",
                                                         "Cutoff",
                                                         "Index2");
const GModelSpectralRegistry     g_spectral_seplaw_registry2(&g_spectral_seplaw_seed2);
#endif
 
/* __ Method name definitions ____________________________________________ */
#define G_MC     "GModelSpectralSuperExpPlaw::mc(GEnergy&, GEnergy&, GTime&,"\
                                                                    " GRan&)"
#define G_READ               "GModelSpectralSuperExpPlaw::read(GXmlElement&)"
#define G_WRITE             "GModelSpectralSuperExpPlaw::write(GXmlElement&)"
 
/* __ Macros _____________________________________________________________ */
 
/* __ Coding definitions _________________________________________________ */
 
/* __ Debug definitions __________________________________________________ */
//#define G_DEBUG_MC                          //!< Debug Monte-Carlo sampling
 
 
/*==========================================================================
 =                                                                         =
 =                        Constructors/destructors                         =
 =                                                                         =
 ==========================================================================*/
 
/***********************************************************************//**
 * @brief Void constructor
 ***************************************************************************/
GModelSpectralSuperExpPlaw::GModelSpectralSuperExpPlaw(void) : GModelSpectral()
{
    // Initialise members
    init_members();
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Model type and parameter name constructor
 *
 * @param[in] type Model type.
 * @param[in] prefactor Name of prefactor parameter.
 * @param[in] index1 Name of index1 parameter.
 * @param[in] pivot Name of pivot parameter.
 * @param[in] cutoff Name of cutoff parameter.
 * @param[in] index2 Name of index2 parameter.
 ***************************************************************************/
GModelSpectralSuperExpPlaw::GModelSpectralSuperExpPlaw(const std::string& type,
                                                       const std::string& prefactor,
                                                       const std::string& index1,
                                                       const std::string& pivot,
                                                       const std::string& cutoff,
                                                       const std::string& index2) :
                            GModelSpectral()
{
    // Initialise members
    init_members();
 
    // Set model type
    m_type = type;
 
    // Set parameter names
    m_norm.name(prefactor);
    m_index1.name(index1);
    m_pivot.name(pivot);
    m_ecut.name(cutoff);
    m_index2.name(index2);
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Constructor
 *
 * @param[in] prefactor Pre factor normalization (ph/cm2/s/MeV).
 * @param[in] index1 Power law index.
 * @param[in] pivot Pivot energy.
 * @param[in] cutoff Cut off energy.
 * @param[in] index2 index of cut off
 *
 * Construct an exponentially cut off power law from
 * - a prefactor value (in units of ph/cm2/s/MeV)
 * - a spectral index,
 * - a pivot energy,
 * - a cut off energy, and
 * - a cut off exponent
 ***************************************************************************/
GModelSpectralSuperExpPlaw::GModelSpectralSuperExpPlaw(const double&  prefactor,
                                                       const double&  index1,
                                                       const GEnergy& pivot,
                                                       const GEnergy& cutoff,
                                                       const double&  index2) :
                            GModelSpectral()
{
    // Initialise members
    init_members();
 
    // Set parameters
    m_norm.value(prefactor);
    m_index1.value(index1);
    m_pivot.value(pivot.MeV()); // Internally stored in MeV
    m_ecut.value(cutoff.MeV()); // Internally stored in MeV
    m_index2.value(index2);
 
    // Autoscale parameters
    autoscale();
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief XML constructor
 *
 * @param[in] xml XML element.
 *
 * Constructs an exponentially cut off power law spectral model by extracting
 * information from an XML element. See the read() method for more
 * information about the expected structure of the XML element.
 ***************************************************************************/
GModelSpectralSuperExpPlaw::GModelSpectralSuperExpPlaw(const GXmlElement& xml) :
                            GModelSpectral()
{
    // Initialise members
    init_members();
 
    // Read information from XML element
    read(xml);
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Copy constructor
 *
 * @param[in] model Super exponentially cut off power law model.
 ***************************************************************************/
GModelSpectralSuperExpPlaw::GModelSpectralSuperExpPlaw(const GModelSpectralSuperExpPlaw& model) :
                            GModelSpectral(model)
{
    // Initialise members
    init_members();
 
    // Copy members
    copy_members(model);
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Destructor
 ***************************************************************************/
GModelSpectralSuperExpPlaw::~GModelSpectralSuperExpPlaw(void)
{
    // Free members
    free_members();
 
    // Return
    return;
}
 
 
/*==========================================================================
 =                                                                         =
 =                                Operators                                =
 =                                                                         =
 ==========================================================================*/
 
/***********************************************************************//**
 * @brief Assignment operator
 *
 * @param[in] model Super exponentially cut off power law model.
 * @return Super exponentially cut off power law model.
 ***************************************************************************/
GModelSpectralSuperExpPlaw& GModelSpectralSuperExpPlaw::operator=(const GModelSpectralSuperExpPlaw& model)
{
    // Execute only if object is not identical
    if (this != &model) {
 
        // Copy base class members
        this->GModelSpectral::operator=(model);
 
        // Free members
        free_members();
 
        // Initialise members
        init_members();
 
        // Copy members
        copy_members(model);
 
    } // endif: object was not identical
 
    // Return
    return *this;
}
 
 
/*==========================================================================
 =                                                                         =
 =                              Public methods                             =
 =                                                                         =
 ==========================================================================*/
 
/***********************************************************************//**
 * @brief Clear exponentially cut off power law model
 ***************************************************************************/
void GModelSpectralSuperExpPlaw::clear(void)
{
    // Free class members (base and derived classes, derived class first)
    free_members();
    this->GModelSpectral::free_members();
 
    // Initialise members
    this->GModelSpectral::init_members();
    init_members();
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Clone super exponentially cut off power law model
 *
 * @return Pointer to deep copy of super exponentially cut off power law model.
 ***************************************************************************/
GModelSpectralSuperExpPlaw* GModelSpectralSuperExpPlaw::clone(void) const
{
    // Clone exponentially cut off power law model
    return new GModelSpectralSuperExpPlaw(*this);
}
 
 
/***********************************************************************//**
 * @brief Evaluate function
 *
 * @param[in] srcEng True photon energy.
 * @param[in] srcTime True photon arrival time.
 * @param[in] gradients Compute gradients?
 * @return Model value (ph/cm2/s/MeV).
 *
 * Evaluates
 *
 * \f[
 *    S_{\rm E}(E | t) = {\tt m\_norm}
 *    \left( \frac{E}{\tt m\_pivot} \right)^{\tt m\_index1}
 *    \exp \left( - \left( \frac{E}{\tt m\_ecut} \right)^{\tt m\_index2}
 *         \right)
 * \f]
 *
 * where
 * - \f${\tt m\_norm}\f$ is the normalization or prefactor,
 * - \f${\tt m\_pivot}\f$ is the pivot energy,
 * - \f${\tt m\_index1}\f$ is the spectral index
 * - \f${\tt m\_ecut}\f$ is the cut off energy, and
 * - \f${\tt m\_index2}\f$ is the index of the cut off.
 *
 * If the @p gradients flag is true the method will also compute the
 * partial derivatives of the model with respect to the parameters using
 *
 * \f[
 *    \frac{\delta S_{\rm E}(E | t)}{\delta {\tt m\_norm}} =
 *      \frac{S_{\rm E}(E | t)}{{\tt m\_norm}}
 * \f]
 *
 * \f[
 *    \frac{\delta S_{\rm E}(E | t)}{\delta {\tt m\_index1}} =
 *      S_{\rm E}(E | t) \, \ln(E/{\tt m_pivot})
 * \f]
 *
 * \f[
 *    \frac{\delta S_{\rm E}(E | t)}{\delta {\tt m\_ecut}} =
 *      S_{\rm E}(E | t) \, \left( \frac{E}{{\tt m\_ecut}^{\tt m\_index2}} \right) \,
 *      \left(\frac{\tt m\_index2}{\tt m\_ecut}\right)
 * \f]
 *
 * \f[
 *    \frac{\delta S_{\rm E}(E | t)}{\delta {\tt m\_index2}} =
 *      -S_{\rm E}(E | t) \, \ln \left(\frac{E}{\tt m\_ecut}\right)\, 
 *        \left(\frac{E}{{\tt m\_ecut}^{\tt m\_index2}} \right)
 * \f]
 *
 * \f[
 *    \frac{\delta S_{\rm E}(E | t)}{\delta {\tt m\_pivot}} =
 *      -S_{\rm E}(E | t) \,
 *      \left( \frac{\tt m\_index}{\tt m\_pivot} \right)
 * \f]
 *
 * @todo The method expects that pivot!=0 and ecut!=0. Otherwise Inf or NaN
 *       may result. We should add a test that prevents using invalid
 *       values.
 ***************************************************************************/
double GModelSpectralSuperExpPlaw::eval(const GEnergy& srcEng,
                                        const GTime&   srcTime,
                                        const bool&    gradients) const
{
    // Update the evaluation cache
    update_eval_cache(srcEng);
 
    // Compute function value
    double value = m_norm.value() * m_last_power;
 
    // Optionally compute gradients
    if (gradients) {
 
        // Compute partial derivatives with respect to the parameter factor
        // values. The partial derivatives with respect to the parameter
        // values are obtained by multiplication with the scale factor.
        double g_norm  = (m_norm.is_free())
                         ? m_norm.scale() * m_last_power
                         : 0.0;
        double g_index1 = (m_index1.is_free())
                          ? value * m_index1.scale() * std::log(m_last_e_norm)
                          : 0.0;
        double g_ecut  = (m_ecut.is_free() && m_ecut.factor_value() != 0.0)
                         ? value * m_last_index2 * m_last_exponent /
                           m_ecut.factor_value()
                         : 0.0;
        double g_pivot = (m_pivot.is_free() && m_pivot.factor_value() != 0.0)
                         ? -value * m_last_index1 / m_pivot.factor_value()
                         : 0.0;
        double g_index2 = (m_index2.is_free())
                          ? -value * m_index2.scale() *
                            std::log(m_last_e_cut) * m_last_exponent
                          : 0.0;
 
        // Set gradients
        m_norm.factor_gradient(g_norm);
        m_index1.factor_gradient(g_index1);
        m_ecut.factor_gradient(g_ecut);
        m_pivot.factor_gradient(g_pivot);
        m_index2.factor_gradient(g_index2);
 
    } // endif: gradient computation was requested
 
    // Compile option: Check for NaN/Inf
    #if defined(G_NAN_CHECK)
    if (gammalib::is_notanumber(value) || gammalib::is_infinite(value)) {
        std::cout << "*** ERROR: GModelSpectralSuperExpPlaw::eval";
        std::cout << "(srcEng=" << srcEng;
        std::cout << ", srcTime=" << srcTime << "):";
        std::cout << " NaN/Inf encountered";
        std::cout << " (value=" << value;
        std::cout << ", power=" << m_last_power;
        std::cout << ")" << std::endl;
    }
    #endif
 
    // Return
    return value;
}
 
 
/***********************************************************************//**
 * @brief Returns model photon flux between [emin, emax] (units: ph/cm2/s)
 *
 * @param[in] emin Minimum photon energy.
 * @param[in] emax Maximum photon energy.
 * @return Photon flux (ph/cm2/s).
 *
 * Computes
 *
 * \f[
 *    \int_{\tt emin}^{\tt emax} S_{\rm E}(E | t) dE
 * \f]
 *
 * where
 * - [@p emin, @p emax] is an energy interval, and
 * - \f$S_{\rm E}(E | t)\f$ is the spectral model (ph/cm2/s/MeV).
 * The integration is done numerically.
 ***************************************************************************/
double GModelSpectralSuperExpPlaw::flux(const GEnergy& emin,
                                        const GEnergy& emax) const
{
    // Initialise flux
    double flux = 0.0;
 
    // Compute only if integration range is valid
    if (emin < emax) {
 
        // Setup integration kernel
        flux_kernel integrand(m_norm.value(),  m_index1.value(),
                              m_pivot.value(), m_ecut.value(),m_index2.value());
        GIntegral integral(&integrand);
 
        // Get integration boundaries in MeV
        double e_min = emin.MeV();
        double e_max = emax.MeV();
 
        // Perform integration
        flux = integral.romberg(e_min, e_max);
 
    } // endif: integration range was valid
 
    // Return
    return flux;
}
 
 
/***********************************************************************//**
 * @brief Returns model energy flux between [emin, emax] (units: erg/cm2/s)
 *
 * @param[in] emin Minimum photon energy.
 * @param[in] emax Maximum photon energy.
 * @return Energy flux (erg/cm2/s).
 *
 * Computes
 *
 * \f[
 *    \int_{\tt emin}^{\tt emax} S_{\rm E}(E | t) E \, dE
 * \f]
 *
 * where
 * - [@p emin, @p emax] is an energy interval, and
 * - \f$S_{\rm E}(E | t)\f$ is the spectral model (ph/cm2/s/MeV).
 * The integration is done numerically.
 ***************************************************************************/
double GModelSpectralSuperExpPlaw::eflux(const GEnergy& emin,
                                         const GEnergy& emax) const
{
    // Initialise flux
    double eflux = 0.0;
 
    // Compute only if integration range is valid
    if (emin < emax) {
 
        // Setup integration kernel
        eflux_kernel integrand(m_norm.value(),  m_index1.value(),
                               m_pivot.value(), m_ecut.value(), m_index2.value());
        GIntegral integral(&integrand);
 
        // Get integration boundaries in MeV
        double e_min = emin.MeV();
        double e_max = emax.MeV();
 
        // Perform integration
        eflux = integral.romberg(e_min, e_max);
 
        // Convert from MeV/cm2/s to erg/cm2/s
        eflux *= gammalib::MeV2erg;
 
    } // endif: integration range was valid
 
    // Return
    return eflux;
}
 
 
/***********************************************************************//**
 * @brief Returns MC energy between [emin, emax]
 *
 * @param[in] emin Minimum photon energy.
 * @param[in] emax Maximum photon energy.
 * @param[in] time True photon arrival time.
 * @param[in,out] ran Random number generator.
 * @return Energy.
 *
 * Simulates a random energy in the interval [emin, emax] for an
 * exponentially cut off power law. The simulation is done using a rejection
 * method. First, a random energy within [emin, emax] is drawn from an
 * power law distribution. Then the energy is accepted or rejected based
 * on an acceptance fraction that is computed from the exponential cut off.
 ***************************************************************************/
GEnergy GModelSpectralSuperExpPlaw::mc(const GEnergy& emin,
                                       const GEnergy& emax,
                                       const GTime&   time,
                                       GRan&          ran) const
{
    // Check energy interval
    gammalib::check_energy_interval(G_MC, emin, emax);
 
    // Allocate energy
    GEnergy energy;
 
    // Update cache
    update_mc_cache(emin, emax);
 
    // Initialise energy
    double eng;
 
    // Initialise acceptance fraction
    double acceptance_fraction;
    double inv_ecut = 1.0 / m_ecut.value();
 
    // Compute random number generator normalisation for speed-up of the
    // computations. Normally it should be sufficient to always use the
    // minimum energy for the normalisation, yet for the case that the model
    // grows with energy we better also test the maximum energy, and we
    // just use the larger of both normalisations
    double norm_emin = std::exp(- std::pow(emin.MeV() * inv_ecut, m_index2.value()));
    double norm_emax = std::exp(- std::pow(emax.MeV() * inv_ecut, m_index2.value()));
    double norm      = (norm_emin > norm_emax) ? norm_emin : norm_emax;
 
    // Debug option: initialise number of samples
    #if defined(G_DEBUG_MC)
    int samples = 0;
    #endif
 
    // Use rejection method to draw a random energy. We first draw
    // analytically from a power law, and then compare the power law
    // at the drawn energy to the exponentially cut off function. This
    // gives an acceptance fraction, and we accept the energy only if
    // a uniform random number is <= the acceptance fraction.
    do {
 
        // Debug option: increment number of samples
        #if defined(G_DEBUG_MC)
        samples++;
        #endif
 
        // Get uniform random number
        double u = ran.uniform();
 
        // Case A: Index is not -1
        if (index1() != -1.0) {
            if (u > 0.0) {
                eng = std::exp(std::log(u * m_mc_pow_ewidth + m_mc_pow_emin) /
                               m_mc_exponent);
            }
            else {
                eng = 0.0;
            }
        }
 
        // Case B: Index is -1
        else {
            eng = std::exp(u * m_mc_pow_ewidth + m_mc_pow_emin);
        }
 
        // Compute acceptance fraction
        acceptance_fraction = std::exp(- std::pow(eng * inv_ecut, m_index2.value()));
 
    } while (ran.uniform() * norm > acceptance_fraction);
 
    // Set energy
    energy.MeV(eng);
 
    // Debug option: write result
    #if defined(G_DEBUG_MC)
    std::cout << "GModelSpectralSuperExpPlaw::mc(";
    std::cout << emin.print() << "," << emax.print() << "," << time.print() << "):";
    std::cout << " energy=" << energy.print();
    std::cout << " samples=" << samples << std::endl;
    #endif
 
    // Return energy
    return energy;
}
 
 
/***********************************************************************//**
 * @brief Read model from XML element
 *
 * @param[in] xml XML element.
 *
 * Reads the spectral information from an XML element.
 ***************************************************************************/
void GModelSpectralSuperExpPlaw::read(const GXmlElement& xml)
{
    // Verify number of model parameters
    gammalib::xml_check_parnum(G_READ, xml, 5);
 
    // Get parameter pointers
    const GXmlElement* norm   = gammalib::xml_get_par(G_READ, xml, m_norm.name());
    const GXmlElement* index1 = gammalib::xml_get_par(G_READ, xml, m_index1.name());
    const GXmlElement* index2 = gammalib::xml_get_par(G_READ, xml, m_index2.name());
    const GXmlElement* ecut   = gammalib::xml_get_par(G_READ, xml, m_ecut.name());
    const GXmlElement* pivot  = gammalib::xml_get_par(G_READ, xml, m_pivot.name());
 
    // Read parameters
    m_norm.read(*norm);
    m_index1.read(*index1);
    m_index2.read(*index2);
    m_ecut.read(*ecut);
    m_pivot.read(*pivot);
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Write model into XML element
 *
 * @param[in] xml XML element.
 *
 * Writes the spectral information into an XML element.
 ***************************************************************************/
void GModelSpectralSuperExpPlaw::write(GXmlElement& xml) const
{
    // Verify model type
    gammalib::xml_check_type(G_WRITE, xml, type());
 
    // Get XML parameters
    GXmlElement* norm   = gammalib::xml_need_par(G_WRITE, xml, m_norm.name());
    GXmlElement* index1 = gammalib::xml_need_par(G_WRITE, xml, m_index1.name());
    GXmlElement* ecut   = gammalib::xml_need_par(G_WRITE, xml, m_ecut.name());
    GXmlElement* index2 = gammalib::xml_need_par(G_WRITE, xml, m_index2.name());
    GXmlElement* pivot  = gammalib::xml_need_par(G_WRITE, xml, m_pivot.name());
 
    // Write parameters
    m_norm.write(*norm);
    m_index1.write(*index1);
    m_ecut.write(*ecut);
    m_index2.write(*index2);
    m_pivot.write(*pivot);
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Print model information
 *
 * @param[in] chatter Chattiness (defaults to NORMAL).
 * @return String containing model information.
 ***************************************************************************/
std::string GModelSpectralSuperExpPlaw::print(const GChatter& chatter) const
{
    // Initialise result string
    std::string result;
 
    // Continue only if chatter is not silent
    if (chatter != SILENT) {
 
        // Append header
        result.append("=== GModelSpectralSuperExpPlaw ===");
 
        // Append information
        result.append("\n"+gammalib::parformat("Number of parameters"));
        result.append(gammalib::str(size()));
        for (int i = 0; i < size(); ++i) {
            result.append("\n"+m_pars[i]->print(chatter));
        }
 
    } // endif: chatter was not silent
 
    // Return result
    return result;
}
 
 
/*==========================================================================
 =                                                                         =
 =                             Private methods                             =
 =                                                                         =
 ==========================================================================*/
 
/***********************************************************************//**
 * @brief Initialise class members
 ***************************************************************************/
void GModelSpectralSuperExpPlaw::init_members(void)
{
    // Initialise model type
    m_type = "SuperExponentialCutoffPowerLaw";
 
    // Initialise powerlaw normalisation
    m_norm.clear();
    m_norm.name("Prefactor");
    m_norm.unit("ph/cm2/s/MeV");
    m_norm.scale(1.0);
    m_norm.value(1.0);          // default: 1.0
    m_norm.min(0.0);            // min:     0.0
    m_norm.free();
    m_norm.gradient(0.0);
    m_norm.has_grad(true);
 
    // Initialise powerlaw index
    m_index1.clear();
    m_index1.name("Index1");
    m_index1.scale(1.0);
    m_index1.value(-2.0);        // default: -2.0
    m_index1.range(-10.0,+10.0); // range:   [-10,+10]
    m_index1.free();
    m_index1.gradient(0.0);
    m_index1.has_grad(true);
 
    // Initialise cut off energy
    m_ecut.clear();
    m_ecut.name("CutoffEnergy");
    m_ecut.unit("MeV");
    m_ecut.scale(1.0);
    m_ecut.value(1000.0);       // default: 1000.0
    m_ecut.min(0.1);            // min:     0.1
    m_ecut.free();
    m_ecut.gradient(0.0);
    m_ecut.has_grad(true);
 
    // Initialise pivot energy
    m_pivot.clear();
    m_pivot.name("PivotEnergy");
    m_pivot.unit("MeV");
    m_pivot.scale(1.0);
    m_pivot.value(100.0);
    m_pivot.fix();
    m_pivot.gradient(0.0);
    m_pivot.has_grad(true);
 
    // Initialise index2
    m_index2.clear();
    m_index2.name("Index2");
    m_index2.scale(1.0);
    m_index2.value(1.0);        // default: -2.0
    m_index2.range(0.0,5.0);    // range:   [0,5]
    m_index2.free();
    m_index2.gradient(0.0);
    m_index2.has_grad(true);
 
    // Set parameter pointer(s)
    m_pars.clear();
    m_pars.push_back(&m_norm);
    m_pars.push_back(&m_index1);
    m_pars.push_back(&m_ecut);
    m_pars.push_back(&m_pivot);
    m_pars.push_back(&m_index2);
 
    // Initialise eval cache
    m_last_energy.clear();
    m_last_index1   = 1.0e30;
    m_last_ecut     = 1.0e30;
    m_last_pivot    = 1.0e30;
    m_last_index2   = 1.0e30;
    m_last_e_norm   = 0.0;
    m_last_e_cut    = 0.0;
    m_last_power    = 0.0;
    m_last_exponent = 0.0;
 
    // Initialise MC cache
    m_mc_emin       = 0.0;
    m_mc_emax       = 0.0;
    m_mc_exponent   = 0.0;
    m_mc_pow_emin   = 0.0;
    m_mc_pow_ewidth = 0.0;
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Copy class members
 *
 * @param[in] model Exponential cut off power law model.
 ***************************************************************************/
void GModelSpectralSuperExpPlaw::copy_members(const GModelSpectralSuperExpPlaw& model)
{
    // Copy members
    m_type   = model.m_type;
    m_norm   = model.m_norm;
    m_index1 = model.m_index1;
    m_ecut   = model.m_ecut;
    m_pivot  = model.m_pivot;
    m_index2 = model.m_index2;
 
    // Set parameter pointer(s)
    m_pars.clear();
    m_pars.push_back(&m_norm);
    m_pars.push_back(&m_index1);
    m_pars.push_back(&m_ecut);
    m_pars.push_back(&m_pivot);
    m_pars.push_back(&m_index2);
 
    // Copy eval cache
    m_last_energy   = model.m_last_energy;
    m_last_index1   = model.m_last_index1;
    m_last_ecut     = model.m_last_ecut;
    m_last_pivot    = model.m_last_pivot;
    m_last_index2   = model.m_last_index2;
    m_last_e_norm   = model.m_last_e_norm;
    m_last_e_cut    = model.m_last_e_cut;
    m_last_power    = model.m_last_power;
    m_last_exponent = model.m_last_exponent;
 
    // Copy MC cache
    m_mc_emin       = model.m_mc_emin;
    m_mc_emax       = model.m_mc_emax;
    m_mc_exponent   = model.m_mc_exponent;
    m_mc_pow_emin   = model.m_mc_pow_emin;
    m_mc_pow_ewidth = model.m_mc_pow_ewidth;
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Delete class members
 ***************************************************************************/
void GModelSpectralSuperExpPlaw::free_members(void)
{
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Update eval precomputation cache
 *
 * @param[in] energy Energy.
 *
 * Updates the precomputation cache for eval() method.
 ***************************************************************************/
void GModelSpectralSuperExpPlaw::update_eval_cache(const GEnergy& energy) const
{
    // Get parameter values (takes 3 multiplications which are difficult
    // to avoid)
    double index1 = m_index1.value();
    double ecut   = m_ecut.value();
    double pivot  = m_pivot.value();
    double index2 = m_index2.value();
 
    // If the energy or one of the parameters index1, index2, cut-off or pivot
    // energy has changed then recompute the cache
    if ((m_last_energy != energy) ||
        (m_last_index1 != index1) ||
        (m_last_ecut   != ecut)   ||
        (m_last_pivot  != pivot)  ||
        (m_last_index2 != index2)) {
 
        // Store actual energy and parameter values
        m_last_energy = energy;
        m_last_index1 = index1;
        m_last_ecut   = ecut;
        m_last_pivot  = pivot;
        m_last_index2 = index2;
 
        // Compute and store value
        double eng      = energy.MeV();
        m_last_e_norm   = eng / m_last_pivot;
        m_last_e_cut    = eng / m_last_ecut;
        m_last_exponent = std::pow(m_last_e_cut, m_last_index2);
        m_last_power    = std::pow(m_last_e_norm, m_last_index1) *
                          std::exp(-m_last_exponent);
 
    } // endif: recomputation was required
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Update Monte Carlo pre computation cache
 *
 * @param[in] emin Minimum photon energy.
 * @param[in] emax Maximum photon energy.
 *
 * Updates the precomputation cache for Monte Carlo simulations.
 ***************************************************************************/
void GModelSpectralSuperExpPlaw::update_mc_cache(const GEnergy& emin,
                                                 const GEnergy& emax) const
 
{
    // Case A: Index is not -1
    if (index1() != -1.0) {
 
        // Change in energy boundaries?
        if (emin.MeV() != m_mc_emin || emax.MeV() != m_mc_emax) {
            m_mc_emin       = emin.MeV();
            m_mc_emax       = emax.MeV();
            m_mc_exponent   = index1() + 1.0;
            m_mc_pow_emin   = std::pow(m_mc_emin, m_mc_exponent);
            m_mc_pow_ewidth = std::pow(m_mc_emax, m_mc_exponent) - m_mc_pow_emin;
        }
 
    }
 
    // Case B: Index is -1
    else {
 
        // Change in energy boundaries?
        if (emin.MeV() != m_mc_emin || emax.MeV() != m_mc_emax) {
            m_mc_emin       = emin.MeV();
            m_mc_emax       = emax.MeV();
            m_mc_exponent   = 0.0;
            m_mc_pow_emin   = std::log(m_mc_emin);
            m_mc_pow_ewidth = std::log(m_mc_emax) - m_mc_pow_emin;
        }
 
    }
 
    // Return
    return;
}
 
 
/***********************************************************************//**
 * @brief Kernel for photon flux integration
 *
 * @param[in] energy Energy (MeV).
 ***************************************************************************/
double GModelSpectralSuperExpPlaw::flux_kernel::eval(const double& energy)
{
    // Evaluate function value
    double e_norm   = energy * m_inv_pivot;
    double e_cut    = energy * m_inv_ecut;
    double exponent = std::pow(e_cut, m_index2);
    double power    = std::pow(e_norm, m_index1) * std::exp(-exponent);
    double value    = m_norm * power;
 
    // Return value
    return value;
}
 
 
/***********************************************************************//**
 * @brief Kernel for energy flux integration
 *
 * @param[in] energy Energy (MeV).
 ***************************************************************************/
double GModelSpectralSuperExpPlaw::eflux_kernel::eval(const double& energy)
{
    // Evaluate function value
    double e_norm   = energy * m_inv_pivot;
    double e_cut    = energy * m_inv_ecut;
    double exponent = std::pow(e_cut, m_index2);
    double power    = std::pow(e_norm, m_index1) * std::exp(-exponent);
    double value    = m_norm * power * energy;
 
    // Return value
    return value;
}