// @(#)root/minuit2:$Id$
// Authors: M. Winkler, F. James, L. Moneta, A. Zsenei   2003-2005

/**********************************************************************
 *                                                                    *
 * Copyright (c) 2005 LCG ROOT Math team,  CERN/PH-SFT                *
 *                                                                    *
 **********************************************************************/

#include "Minuit2/HessianGradientCalculator.h"
#include "Minuit2/InitialGradientCalculator.h"
#include "Minuit2/MnFcn.h"
#include "Minuit2/MnUserTransformation.h"
#include "Minuit2/MnMachinePrecision.h"
#include "Minuit2/MinimumParameters.h"
#include "Minuit2/FunctionGradient.h"
#include "Minuit2/MnStrategy.h"
#include "Minuit2/MnPrint.h"
#include "Minuit2/MPIProcess.h"

#include <cmath>
#include <cassert>

namespace ROOT {

namespace Minuit2 {

FunctionGradient HessianGradientCalculator::operator()(const MinimumParameters &par) const
{
   // use initial gradient as starting point
   InitialGradientCalculator gc(fFcn, fTransformation);
   FunctionGradient gra = gc(par);

   return (*this)(par, gra);
}

FunctionGradient HessianGradientCalculator::
operator()(const MinimumParameters &par, const FunctionGradient &Gradient) const
{
   // interface of the base class. Use DeltaGradient for op.
   std::pair<FunctionGradient, MnAlgebraicVector> mypair = DeltaGradient(par, Gradient);

   return mypair.first;
}

const MnMachinePrecision &HessianGradientCalculator::Precision() const
{
   // return the precision
   return fTransformation.Precision();
}

unsigned int HessianGradientCalculator::Ncycle() const
{
   // return number of calculation cycles (defined in strategy)
   return Strategy().HessianGradientNCycles();
}

std::pair<FunctionGradient, MnAlgebraicVector>
HessianGradientCalculator::DeltaGradient(const MinimumParameters &par, const FunctionGradient &Gradient) const
{
   // calculate gradient for Hessian
   assert(par.IsValid());

   MnPrint print("HessianGradientCalculator");

   MnAlgebraicVector x = par.Vec();
   MnAlgebraicVector grd = Gradient.Grad();
   const MnAlgebraicVector &g2 = Gradient.G2();
   // const MnAlgebraicVector& gstep = Gradient.Gstep();
   // update also gradient step sizes
   MnAlgebraicVector gstep = Gradient.Gstep();

   double fcnmin = par.Fval();
   //   std::cout<<"fval: "<<fcnmin<<std::endl;

   double dfmin = 4. * Precision().Eps2() * (fabs(fcnmin) + Fcn().Up());

   unsigned int n = x.size();
   MnAlgebraicVector dgrd(n);

   MPIProcess mpiproc(n, 0);
   // initial starting values
   unsigned int startElementIndex = mpiproc.StartElementIndex();
   unsigned int endElementIndex = mpiproc.EndElementIndex();

   for (unsigned int i = startElementIndex; i < endElementIndex; i++) {
      double xtf = x(i);
      double dmin = 4. * Precision().Eps2() * (xtf + Precision().Eps2());
      double epspri = Precision().Eps2() + fabs(grd(i) * Precision().Eps2());
      double optstp = sqrt(dfmin / (fabs(g2(i)) + epspri));
      double d = 0.2 * fabs(gstep(i));
      if (d > optstp)
         d = optstp;
      if (d < dmin)
         d = dmin;
      double chgold = 10000.;
      double dgmin = 0.;
      double grdold = 0.;
      double grdnew = 0.;
      for (unsigned int j = 0; j < Ncycle(); j++) {
         x(i) = xtf + d;
         double fs1 = Fcn()(x);
         x(i) = xtf - d;
         double fs2 = Fcn()(x);
         x(i) = xtf;
         //       double sag = 0.5*(fs1+fs2-2.*fcnmin);
         // LM: should I calculate also here second derivatives ???

         grdold = grd(i);
         grdnew = (fs1 - fs2) / (2. * d);
         dgmin = Precision().Eps() * (std::fabs(fs1) + std::fabs(fs2)) / d;
         // if(fabs(grdnew) < Precision().Eps()) break;
         if (grdnew == 0)
            break;
         double change = fabs((grdold - grdnew) / grdnew);
         if (change > chgold && j > 1)
            break;
         chgold = change;
         grd(i) = grdnew;
         // LM : update also the step sizes
         gstep(i) = d;

         if (change < 0.05)
            break;
         if (fabs(grdold - grdnew) < dgmin)
            break;
         if (d < dmin)
            break;
         d *= 0.2;
      }

      dgrd(i) = std::max(dgmin, std::fabs(grdold - grdnew));

      print.Debug("HGC Param :", i, "\t new g1 =", grd(i), "gstep =", d, "dgrd =", dgrd(i));
   }

   mpiproc.SyncVector(grd);
   mpiproc.SyncVector(gstep);
   mpiproc.SyncVector(dgrd);

   return std::pair<FunctionGradient, MnAlgebraicVector>(FunctionGradient(grd, g2, gstep), dgrd);
}

} // namespace Minuit2

} // namespace ROOT
