MEQCD2to2Fast.h
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MEQCD2to2Fast.h
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	// -- C++ --
	//
	// MEQCD2to2Fast.h is a part of Herwig++ - A multi-purpose Monte Carlo event generator
	// Copyright (C) 2002-2007 The Herwig Collaboration
	//
	// Herwig++ is licenced under version 2 of the GPL, see COPYING for details.
	// Please respect the MCnet academic guidelines, see GUIDELINES for details.
	//
	#ifndef HERWIG_MEQCD2to2Fast_H
	#define HERWIG_MEQCD2to2Fast_H
	//
	// This is the declaration of the MEQCD2to2Fast class.
	//

	#include "Herwig++/MatrixElement/HwME2to2Base.h"
	#include "ThePEG/Repository/UseRandom.h"

	namespace Herwig {
	using namespace ThePEG;
	using namespace ThePEG::Helicity;

	/**
	* The MEQCD2to2Fast class implements the matrix elements for
	* QCD \f$2\to2\f$ scattering processes using hard coded formulae and
	* as such can not include spin correlations. It is designed to be a faster
	* replacement for MEQCD2to2 for use in the underlying event.
	*
	* @see \ref MEQCD2to2FastInterfaces "The interfaces"
	* defined for MEQCD2to2Fast.
	*/
	class MEQCD2to2Fast: public HwME2to2Base {

	public:

	/**
	* The default constructor.
	*/
	inline MEQCD2to2Fast();

	/** @name Virtual functions required by the MEBase class. */
	//@{
	/**
	* Return the order in \f$\alpha_S\f$ in which this matrix
	* element is given.
	*/
	virtual unsigned int orderInAlphaS() const;

	/**
	* Return the order in \f$\alpha_{EW}\f$ in which this matrix
	* element is given.
	*/
	virtual unsigned int orderInAlphaEW() const;

	/**
	* The matrix element for the kinematical configuration
	* previously provided by the last call to setKinematics(), suitably
	* scaled by sHat() to give a dimension-less number.
	* @return the matrix element scaled with sHat() to give a
	* dimensionless number.
	*/
	virtual double me2() const;

	/**
	* Return the scale associated with the last set phase space point.
	*/
	virtual Energy2 scale() const;

	/**
	* Add all possible diagrams with the add() function.
	*/
	virtual void getDiagrams() const;

	/**
	* Get diagram selector. With the information previously supplied with the
	* setKinematics method, a derived class may optionally
	* override this method to weight the given diagrams with their
	* (although certainly not physical) relative probabilities.
	* @param dv the diagrams to be weighted.
	* @return a Selector relating the given diagrams to their weights.
	*/
	virtual Selector<DiagramIndex> diagrams(const DiagramVector & dv) const;

	/**
	* Return a Selector with possible colour geometries for the selected
	* diagram weighted by their relative probabilities.
	* @param diag the diagram chosen.
	* @return the possible colour geometries weighted by their
	* relative probabilities.
	*/
	virtual Selector<const ColourLines *>
	colourGeometries(tcDiagPtr diag) const;
	//@}


	public:

	/** @name Functions used by the persistent I/O system. */
	//@{
	/**
	* Function used to write out object persistently.
	* @param os the persistent output stream written to.
	*/
	void persistentOutput(PersistentOStream & os) const;

	/**
	* Function used to read in object persistently.
	* @param is the persistent input stream read from.
	* @param version the version number of the object when written.
	*/
	void persistentInput(PersistentIStream & is, int version);
	//@}

	/**
	* The standard Init function used to initialize the interfaces.
	* Called exactly once for each class by the class description system
	* before the main function starts or
	* when this class is dynamically loaded.
	*/
	static void Init();

	protected:

	/**
	* Members to calculate the matrix elements
	*/
	//@{
	/**
	* Matrix element for \f$gg\to gg\f$.
	*/
	inline double gg2ggME() const;

	/**
	* Matrix element for \f$gg\to q\bar{q}\f$
	*/
	inline double gg2qqbarME() const;

	/**
	* Matrix element for \f$q\bar{q}\to gg\f$
	*/
	inline double qqbar2ggME() const;

	/**
	* Matrix element for \f$qg\to qg\f$
	*/
	inline double qg2qgME() const;

	/**
	* Matrix elements for \f$\bar{q}g\to \bar{q}g\f$.
	*/
	inline double qbarg2qbargME() const;

	/**
	* Matrix element for \f$qq\to qq\f$
	*/
	inline double qq2qqME() const;

	/**
	* Matrix element for \f$\bar{q}\bar{q}\to \bar{q}\bar{q}\f$
	*/
	inline double qbarqbar2qbarqbarME() const;

	/**
	* Matrix element for \f$q\bar{q}\to q\bar{q}\f$
	*/
	inline double qqbar2qqbarME() const;
	//@}

	protected:

	/** @name Clone Methods. */
	//@{
	/**
	* Make a simple clone of this object.
	* @return a pointer to the new object.
	*/
	inline virtual IBPtr clone() const;

	/** Make a clone of this object, possibly modifying the cloned object
	* to make it sane.
	* @return a pointer to the new object.
	*/
	inline virtual IBPtr fullclone() const;
	//@}

	private:

	/**
	* The static object used to initialize the description of this class.
	* Indicates that this is a concrete class with persistent data.
	*/
	static ClassDescription<MEQCD2to2Fast> initMEQCD2to2Fast;

	/**
	* The assignment operator is private and must never be called.
	* In fact, it should not even be implemented.
	*/
	MEQCD2to2Fast & operator=(const MEQCD2to2Fast &);

	private:

	/**
	* Maximum numbere of quark flavours to include
	*/
	unsigned int _maxflavour;

	/**
	* Processes to include
	*/
	unsigned int _process;

	/**
	* Colour flow
	*/
	mutable unsigned int _flow;

	/**
	* Diagram
	*/
	mutable unsigned int _diagram;
	};

	}

	#include "ThePEG/Utilities/ClassTraits.h"

	namespace ThePEG {

	/** @cond TRAITSPECIALIZATIONS */

	/** This template specialization informs ThePEG about the
	* base classes of MEQCD2to2Fast. */
	template <>
	struct BaseClassTrait<Herwig::MEQCD2to2Fast,1> {
	/** Typedef of the first base class of MEQCD2to2Fast. */
	typedef Herwig::HwME2to2Base NthBase;
	};

	/** This template specialization informs ThePEG about the name of
	* the MEQCD2to2Fast class and the shared object where it is defined. */
	template <>
	struct ClassTraits<Herwig::MEQCD2to2Fast>
	: public ClassTraitsBase<Herwig::MEQCD2to2Fast> {
	/** Return a platform-independent class name */
	static string className() { return "Herwig::MEQCD2to2Fast"; }
	/**
	* The name of a file containing the dynamic library where the class
	* MEQCD2to2Fast is implemented. It may also include several, space-separated,
	* libraries if the class MEQCD2to2Fast depends on other classes (base classes
	* excepted). In this case the listed libraries will be dynamically
	* linked in the order they are specified.
	*/
	static string library() { return "HwMEHadronFast.so"; }
	};

	/** @endcond */

	}

	#include "MEQCD2to2Fast.icc"

	#endif /* HERWIG_MEQCD2to2Fast_H */

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