/**
 *  \file IMP/isd/vonMisesKappaConjugateRestraint.h
 *  \brief Conjugate prior for \f$\kappa\f$ in the von Mises distribution.
 *
 *  Copyright 2007-2013 IMP Inventors. All rights reserved.
 *
 */

#ifndef IMPISD_VON_MISES_KAPPA_CONJUGATE_RESTRAINT_H
#define IMPISD_VON_MISES_KAPPA_CONJUGATE_RESTRAINT_H

#include <IMP/isd/isd_config.h>
#include <IMP/SingletonScore.h>
#include "ISDRestraint.h"
#include <IMP/restraint_macros.h>

IMPISD_BEGIN_NAMESPACE

//! Conjugate prior for the concentration parameter of a von Mises distribution.
/** \f[ p(\kappa|c,R_0) = \frac{\exp(\kappa R_0)}{I_0(\kappa)^c} \f]
    \f$0 < R_0 \le c\f$
    where \f$kappa\f$ is the concentration parameter.
    Default values: \f$R_0=1\f$ and \f$c=10\f$
 */
class IMPISDEXPORT vonMisesKappaConjugateRestraint : public ISDRestraint
{
  Pointer<Particle> kappa_;
  double old_kappaval;
  bool bessel_init_;
  double I0_,I1_;
  double c_,R0_;

public:
  //! Create the restraint.
  vonMisesKappaConjugateRestraint(Particle *kappa, double c=10.0,
                                  double R0=0.0);

  /** This macro declares the basic needed methods: evaluate and show
   */
  IMP_RESTRAINT(vonMisesKappaConjugateRestraint);

  virtual double get_probability() const;

private:

  void update_bessel(double kappaval); // update memoized bessel value
  double get_kappa() const;

};

IMPISD_END_NAMESPACE

#endif  /* IMPISD_VON_MISES_KAPPA_CONJUGATE_RESTRAINT_H */