FNormal.h

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/**
 *  \file IMP/isd/FNormal.h    \brief Normal distribution of Function
 *
 *  Copyright 2007-2014 IMP Inventors. All rights reserved.
 */

#ifndef IMPISD_FNORMAL_H
#define IMPISD_FNORMAL_H

#include <IMP/isd/isd_config.h>
#include <IMP/macros.h>
#include <IMP/kernel/Model.h>
#include <IMP/constants.h>
#include <math.h>

IMPISD_BEGIN_NAMESPACE

//! FNormal
/** Probability density function and -log(p) of normal sampling from some
 * function F. If A is drawn from the F-Normal distribution then F(A) is drawn
 * from a normal distribution with mean M and standard deviation sigma.
 * Arguments: F(A), J(A) the derivative of F w/r to A, F(M) and sigma.  The
 * distribution is normalized with respect to the variable A.
 *
 *  Example: if F is the log function, the F-normal distribution is the
 *  lognormal distribution with mean M and standard deviation sigma.
 *
 *  NOTE: for now, F must be monotonically increasing, so that JA > 0. The
 *  program will not check for that.
 */

class IMPISDEXPORT FNormal : public base::Object {
 public:
  FNormal(double FA, double JA, double FM, double sigma)
      : base::Object("FNormal %1%"), FA_(FA), JA_(JA), FM_(FM), sigma_(sigma) {}

  /* energy (score) functions, aka -log(p) */
  virtual double evaluate() const {
    return -log(JA_ / sigma_) + 0.5 * log(2 * IMP::PI) +
           1 / (2 * square(sigma_)) * square(FA_ - FM_);
  }

  // derivative of score wrt F(A)
  virtual double evaluate_derivative_FA() const {
    return (FA_ - FM_) / square(sigma_);
  }

  virtual double evaluate_derivative_JA() const { return -1 / JA_; }

  // derivative wrt F(M)
  virtual double evaluate_derivative_FM() const {
    return (FM_ - FA_) / square(sigma_);
  }

  virtual double evaluate_derivative_sigma() const {
    return 1 / sigma_ - square(FA_ - FM_) / pow(sigma_, 3);
  }

  /* probability density function */
  virtual double density() const {
    return JA_ / (sqrt(2 * IMP::PI) * sigma_) *
           exp(-square(FA_ - FM_) / (2 * square(sigma_)));
  }

  /* change of parameters */
  void set_FA(double f) { FA_ = f; }
  void set_JA(double f) { JA_ = f; }
  void set_FM(double f) { FM_ = f; }
  void set_sigma(double f) { sigma_ = f; }

  IMP_OBJECT_METHODS(FNormal);
  /*IMP_OBJECT_INLINE(FNormal, out << "FNormal: " << FA_ << ", " << JA_
    << ", " << FM_ << ", " << sigma_ <<std::endl, {});*/

 private:
  double FA_, JA_, FM_, sigma_;
};

IMPISD_END_NAMESPACE

#endif /* IMPISD_FNORMAL_H */