/*************************************************************************************

Grid physics library, www.github.com/paboyle/Grid

Source file: ./lib/qcd/action/pseudofermion/ExactOneFlavourRatio.h

Copyright (C) 2017

Author: Peter Boyle <paboyle@ph.ed.ac.uk>
Author: David Murphy <dmurphy@phys.columbia.edu>

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

See the full license in the file "LICENSE" in the top level distribution directory
*************************************************************************************/
			   /*  END LEGAL */

			   /////////////////////////////////////////////////////////////////
			   // Implementation of exact one flavour algorithm (EOFA)         //
			   // using fermion classes defined in:                           //
			   //    Grid/qcd/action/fermion/DomainWallEOFAFermion.h (Shamir) //
			   //    Grid/qcd/action/fermion/MobiusEOFAFermion.h (Mobius)     //
			   // arXiv: 1403.1683, 1706.05843                                //
			   /////////////////////////////////////////////////////////////////

#ifndef QCD_PSEUDOFERMION_EXACT_ONE_FLAVOUR_RATIO_H
#define QCD_PSEUDOFERMION_EXACT_ONE_FLAVOUR_RATIO_H

NAMESPACE_BEGIN(Grid);

///////////////////////////////////////////////////////////////
// Exact one flavour implementation of DWF determinant ratio //
///////////////////////////////////////////////////////////////

template<class Impl>
class ExactOneFlavourRatioPseudoFermionAction : public Action<typename Impl::GaugeField>
{
public:
  INHERIT_IMPL_TYPES(Impl);
  typedef OneFlavourRationalParams Params;
  Params param;
  MultiShiftFunction PowerNegHalf;

private:
  bool use_heatbath_forecasting;
  AbstractEOFAFermion<Impl>& Lop; // the basic LH operator
  AbstractEOFAFermion<Impl>& Rop; // the basic RH operator
  SchurRedBlackDiagMooeeSolve<FermionField> Solver;
  FermionField Phi; // the pseudofermion field for this trajectory

public:
  ExactOneFlavourRatioPseudoFermionAction(AbstractEOFAFermion<Impl>& _Lop, AbstractEOFAFermion<Impl>& _Rop,
					  OperatorFunction<FermionField>& S, Params& p, bool use_fc=false) : Lop(_Lop), Rop(_Rop), Solver(S),
													     Phi(_Lop.FermionGrid()), param(p), use_heatbath_forecasting(use_fc)
  {
    AlgRemez remez(param.lo, param.hi, param.precision);

    // MdagM^(+- 1/2)
    std::cout << GridLogMessage << "Generating degree " << param.degree << " for x^(-1/2)" << std::endl;
    remez.generateApprox(param.degree, 1, 2);
    PowerNegHalf.Init(remez, param.tolerance, true);
  };

  virtual std::string action_name() { return "ExactOneFlavourRatioPseudoFermionAction"; }

  virtual std::string LogParameters() {
    std::stringstream sstream;
    sstream << GridLogMessage << "[" << action_name() << "] Low            :" << param.lo << std::endl;
    sstream << GridLogMessage << "[" << action_name() << "] High           :" << param.hi << std::endl;
    sstream << GridLogMessage << "[" << action_name() << "] Max iterations :" << param.MaxIter << std::endl;
    sstream << GridLogMessage << "[" << action_name() << "] Tolerance      :" << param.tolerance << std::endl;
    sstream << GridLogMessage << "[" << action_name() << "] Degree         :" << param.degree << std::endl;
    sstream << GridLogMessage << "[" << action_name() << "] Precision      :" << param.precision << std::endl;
    return sstream.str();
  }

  // Spin projection
  void spProj(const FermionField& in, FermionField& out, int sign, int Ls)
  {
    if(sign == 1){ for(int s=0; s<Ls; ++s){ axpby_ssp_pplus(out, 0.0, in, 1.0, in, s, s); } }
    else{ for(int s=0; s<Ls; ++s){ axpby_ssp_pminus(out, 0.0, in, 1.0, in, s, s); } }
  }

  // EOFA heatbath: see Eqn. (29) of arXiv:1706.05843
  // We generate a Gaussian noise vector \eta, and then compute
  //  \Phi = M_{\rm EOFA}^{-1/2} * \eta
  // using a rational approximation to the inverse square root
  virtual void refresh(const GaugeField& U, GridParallelRNG& pRNG)
  {
    Lop.ImportGauge(U);
    Rop.ImportGauge(U);

    FermionField eta         (Lop.FermionGrid());
    FermionField CG_src      (Lop.FermionGrid());
    FermionField CG_soln     (Lop.FermionGrid());
    FermionField Forecast_src(Lop.FermionGrid());
    std::vector<FermionField> tmp(2, Lop.FermionGrid());

    // Use chronological inverter to forecast solutions across poles
    std::vector<FermionField> prev_solns;
    if(use_heatbath_forecasting){ prev_solns.reserve(param.degree); }
    ChronoForecast<AbstractEOFAFermion<Impl>, FermionField> Forecast;

    // Seed with Gaussian noise vector (var = 0.5)
    RealD scale = std::sqrt(0.5);
    gaussian(pRNG,eta);
    eta = eta * scale;
    printf("Heatbath source vector: <\\eta|\\eta> = %1.15e\n", norm2(eta));

    // \Phi = ( \alpha_{0} + \sum_{k=1}^{N_{p}} \alpha_{l} * \gamma_{l} ) * \eta
    RealD N(PowerNegHalf.norm);
    for(int k=0; k<param.degree; ++k){ N += PowerNegHalf.residues[k] / ( 1.0 + PowerNegHalf.poles[k] ); }
    Phi = eta * N;

    // LH terms:
    // \Phi = \Phi + k \sum_{k=1}^{N_{p}} P_{-} \Omega_{-}^{\dagger} ( H(mf)
    //          - \gamma_{l} \Delta_{-}(mf,mb) P_{-} )^{-1} \Omega_{-} P_{-} \eta
    RealD gamma_l(0.0);
    spProj(eta, tmp[0], -1, Lop.Ls);
    Lop.Omega(tmp[0], tmp[1], -1, 0);
    G5R5(CG_src, tmp[1]);
    tmp[1] = Zero();
    for(int k=0; k<param.degree; ++k){
      gamma_l = 1.0 / ( 1.0 + PowerNegHalf.poles[k] );
      Lop.RefreshShiftCoefficients(-gamma_l);
      if(use_heatbath_forecasting){ // Forecast CG guess using solutions from previous poles
	Lop.Mdag(CG_src, Forecast_src);
	CG_soln = Forecast(Lop, Forecast_src, prev_solns);
	Solver(Lop, CG_src, CG_soln);
	prev_solns.push_back(CG_soln);
      } else {
	CG_soln = Zero(); // Just use zero as the initial guess
	Solver(Lop, CG_src, CG_soln);
      }
      Lop.Dtilde(CG_soln, tmp[0]); // We actually solved Cayley preconditioned system: transform back
      tmp[1] = tmp[1] + ( PowerNegHalf.residues[k]*gamma_l*gamma_l*Lop.k ) * tmp[0];
    }
    Lop.Omega(tmp[1], tmp[0], -1, 1);
    spProj(tmp[0], tmp[1], -1, Lop.Ls);
    Phi = Phi + tmp[1];

    // RH terms:
    // \Phi = \Phi - k \sum_{k=1}^{N_{p}} P_{+} \Omega_{+}^{\dagger} ( H(mb)
    //          + \gamma_{l} \Delta_{+}(mf,mb) P_{+} )^{-1} \Omega_{+} P_{+} \eta
    spProj(eta, tmp[0], 1, Rop.Ls);
    Rop.Omega(tmp[0], tmp[1], 1, 0);
    G5R5(CG_src, tmp[1]);
    tmp[1] = Zero();
    if(use_heatbath_forecasting){ prev_solns.clear(); } // empirically, LH solns don't help for RH solves
    for(int k=0; k<param.degree; ++k){
      gamma_l = 1.0 / ( 1.0 + PowerNegHalf.poles[k] );
      Rop.RefreshShiftCoefficients(-gamma_l*PowerNegHalf.poles[k]);
      if(use_heatbath_forecasting){
	Rop.Mdag(CG_src, Forecast_src);
	CG_soln = Forecast(Rop, Forecast_src, prev_solns);
	Solver(Rop, CG_src, CG_soln);
	prev_solns.push_back(CG_soln);
      } else {
	CG_soln = Zero();
	Solver(Rop, CG_src, CG_soln);
      }
      Rop.Dtilde(CG_soln, tmp[0]); // We actually solved Cayley preconditioned system: transform back
      tmp[1] = tmp[1] - ( PowerNegHalf.residues[k]*gamma_l*gamma_l*Rop.k ) * tmp[0];
    }
    Rop.Omega(tmp[1], tmp[0], 1, 1);
    spProj(tmp[0], tmp[1], 1, Rop.Ls);
    Phi = Phi + tmp[1];

    // Reset shift coefficients for energy and force evals
    Lop.RefreshShiftCoefficients(0.0);
    Rop.RefreshShiftCoefficients(-1.0);
  };

  // EOFA action: see Eqn. (10) of arXiv:1706.05843
  virtual RealD S(const GaugeField& U)
  {
    Lop.ImportGauge(U);
    Rop.ImportGauge(U);

    FermionField spProj_Phi(Lop.FermionGrid());
    std::vector<FermionField> tmp(2, Lop.FermionGrid());

    // S = <\Phi|\Phi>
    RealD action(norm2(Phi));

    // LH term: S = S - k <\Phi| P_{-} \Omega_{-}^{\dagger} H(mf)^{-1} \Omega_{-} P_{-} |\Phi>
    spProj(Phi, spProj_Phi, -1, Lop.Ls);
    Lop.Omega(spProj_Phi, tmp[0], -1, 0);
    G5R5(tmp[1], tmp[0]);
    tmp[0] = Zero();
    Solver(Lop, tmp[1], tmp[0]);
    Lop.Dtilde(tmp[0], tmp[1]); // We actually solved Cayley preconditioned system: transform back
    Lop.Omega(tmp[1], tmp[0], -1, 1);
    action -= Lop.k * innerProduct(spProj_Phi, tmp[0]).real();

    // RH term: S = S + k <\Phi| P_{+} \Omega_{+}^{\dagger} ( H(mb)
    //               - \Delta_{+}(mf,mb) P_{+} )^{-1} \Omega_{-} P_{-} |\Phi>
    spProj(Phi, spProj_Phi, 1, Rop.Ls);
    Rop.Omega(spProj_Phi, tmp[0], 1, 0);
    G5R5(tmp[1], tmp[0]);
    tmp[0] = Zero();
    Solver(Rop, tmp[1], tmp[0]);
    Rop.Dtilde(tmp[0], tmp[1]);
    Rop.Omega(tmp[1], tmp[0], 1, 1);
    action += Rop.k * innerProduct(spProj_Phi, tmp[0]).real();

    return action;
  };

  // EOFA pseudofermion force: see Eqns. (34)-(36) of arXiv:1706.05843
  virtual void deriv(const GaugeField& U, GaugeField& dSdU)
  {
    Lop.ImportGauge(U);
    Rop.ImportGauge(U);

    FermionField spProj_Phi      (Lop.FermionGrid());
    FermionField Omega_spProj_Phi(Lop.FermionGrid());
    FermionField CG_src          (Lop.FermionGrid());
    FermionField Chi             (Lop.FermionGrid());
    FermionField g5_R5_Chi       (Lop.FermionGrid());

    GaugeField force(Lop.GaugeGrid());

    // LH: dSdU = k \chi_{L}^{\dagger} \gamma_{5} R_{5} ( \partial_{x,\mu} D_{w} ) \chi_{L}
    //     \chi_{L} = H(mf)^{-1} \Omega_{-} P_{-} \Phi
    spProj(Phi, spProj_Phi, -1, Lop.Ls);
    Lop.Omega(spProj_Phi, Omega_spProj_Phi, -1, 0);
    G5R5(CG_src, Omega_spProj_Phi);
    spProj_Phi = Zero();
    Solver(Lop, CG_src, spProj_Phi);
    Lop.Dtilde(spProj_Phi, Chi);
    G5R5(g5_R5_Chi, Chi);
    Lop.MDeriv(force, g5_R5_Chi, Chi, DaggerNo);
    dSdU = Lop.k * force;

    // RH: dSdU = dSdU - k \chi_{R}^{\dagger} \gamma_{5} R_{5} ( \partial_{x,\mu} D_{w} ) \chi_{}
    //     \chi_{R} = ( H(mb) - \Delta_{+}(mf,mb) P_{+} )^{-1} \Omega_{+} P_{+} \Phi
    spProj(Phi, spProj_Phi, 1, Rop.Ls);
    Rop.Omega(spProj_Phi, Omega_spProj_Phi, 1, 0);
    G5R5(CG_src, Omega_spProj_Phi);
    spProj_Phi = Zero();
    Solver(Rop, CG_src, spProj_Phi);
    Rop.Dtilde(spProj_Phi, Chi);
    G5R5(g5_R5_Chi, Chi);
    Lop.MDeriv(force, g5_R5_Chi, Chi, DaggerNo);
    dSdU = dSdU - Rop.k * force;
  };
};

NAMESPACE_END(Grid);

#endif