Dipole/Kernels/ColourMatrixElementCorrection.h

0001 // -*- C++ -*-
0002 //
0003 // ColourMatrixElementCorrection.h is a part of Herwig - A multi-purpose Monte Carlo event generator
0004 // Copyright (C) 2002-2019 The Herwig Collaboration
0005 //
0006 // Herwig is licenced under version 2 of the GPL, see COPYING for details.
0007 // Please respect the MCnet academic guidelines, see GUIDELINES for details.
0008 //
0009 #ifndef Herwig_ColourMatrixElementCorrection_H
0010 #define Herwig_ColourMatrixElementCorrection_H
0011 //
0012 // This is the declaration of the ColourMatrixElementCorrection class.
0013 //
0014
0015 #include "Herwig/Shower/Dipole/Base/DipoleSplittingReweight.h"
0016
0017 #include <tuple>
0018
0019 namespace Herwig {
0020
0021 using namespace ThePEG;
0022
0023 /**
0024  * \ingroup DipoleShower
0025  * \author Johan Thoren, Simon Platzer
0026  *
0027  * \brief ColourMatrixElementCorrection is implementing colour matrix element
0028  * corrections through the weighted Sudakov algorithm
0029  *
0030  * @see \ref ColourMatrixElementCorrectionInterfaces "The interfaces"
0031  * defined for ColourMatrixElementCorrection.
0032  */
0033 class ColourMatrixElementCorrection: public DipoleSplittingReweight {
0034
0035 public:
0036
0037   /**
0038    * The default constructor.
0039    */
0040   ColourMatrixElementCorrection();
0041
0042 public:
0043
0044   /**
0045    * Calculate and cache the colour matrix element correction factor
0046    * for the given splitting type.
0047    */
0048   double cmec(const DipoleSplittingInfo&) const;
0049
0050   /**
0051    * Return the reweighting factor for the given splitting type.
0052    */
0053   virtual double evaluate(const DipoleSplittingInfo& s) const {
0054     return cmec(s);
0055   }
0056
0057   /**
0058    * Return the absolute value of the colour matrix element correction
0059    * as an enhancement hint for the sampling of the un-reweighted
0060    * splitting kernel.
0061    */
0062   virtual double hint(const DipoleSplittingInfo& s) const {
0063     if ( hintOnly(s) )
0064       return cmec(s);
0065     return abs(cmec(s))*lambda;
0066   }
0067
0068   /**
0069    * Return true, if the reweight can be entirely absorbed into the hint. A
0070    * possible detuning will be switched off.
0071    */
0072   virtual bool hintOnly(const DipoleSplittingInfo& s) const {
0073     return cmec(s) > 0.;
0074   }
0075
0076   /**
0077    * Set the factor in front of enhance used by the veto algorithm.
0078    */
0079   virtual void reweightFactor(const double c) {
0080     assert(c > 0.0);
0081     lambda = c;
0082   }
0083
0084   /**
0085    * Set the factor in front of enhance used by the veto algorithm.
0086    */
0087   virtual void negativeScaling(const double c) {
0088     assert(c >= 0.0);
0089     negCMECScaling = c;
0090   }
0091
0092 public:
0093
0094   /** @name Functions used by the persistent I/O system. */
0095   //@{
0096   /**
0097    * Function used to write out object persistently.
0098    * @param os the persistent output stream written to.
0099    */
0100   void persistentOutput(PersistentOStream & os) const;
0101
0102   /**
0103    * Function used to read in object persistently.
0104    * @param is the persistent input stream read from.
0105    * @param version the version number of the object when written.
0106    */
0107   void persistentInput(PersistentIStream & is, int version);
0108   //@}
0109
0110   /**
0111    * The standard Init function used to initialize the interfaces.
0112    * Called exactly once for each class by the class description system
0113    * before the main function starts or
0114    * when this class is dynamically loaded.
0115    */
0116   static void Init();
0117
0118 protected:
0119
0120   /** @name Clone Methods. */
0121   //@{
0122   /**
0123    * Make a simple clone of this object.
0124    * @return a pointer to the new object.
0125    */
0126   virtual IBPtr clone() const;
0127
0128   /** Make a clone of this object, possibly modifying the cloned object
0129    * to make it sane.
0130    * @return a pointer to the new object.
0131    */
0132   virtual IBPtr fullclone() const;
0133   //@}
0134
0135 // If needed, insert declarations of virtual function defined in the
0136 // InterfacedBase class here (using ThePEG-interfaced-decl in Emacs).
0137
0138 private:
0139
0140   /**
0141    * Factor to shuffle the magnitude of the CMEC between the splitting kernel
0142    * and the weight in the reweighted veto algorithm.
0143    */
0144   double lambda;
0145
0146   /**
0147    * Scaling factor multiplying all of the negative colour matrix element
0148    * corrections. The physically sensible value is 1.0, but this factor can
0149    * be used to examine the effects of the negative contributions.
0150    */
0151   double negCMECScaling;
0152
0153   /**
0154    * The assignment operator is private and must never be called.
0155    * In fact, it should not even be implemented.
0156    */
0157   ColourMatrixElementCorrection & operator=(const ColourMatrixElementCorrection &) = delete;
0158
0159 };
0160
0161 }
0162
0163 #endif /* Herwig_ColourMatrixElementCorrection_H */