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

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

    Source file: ./lib/algorithms/iterative/ConjugateResidual.h

    Copyright (C) 2015

Author: Azusa Yamaguchi <ayamaguc@staffmail.ed.ac.uk>
Author: Peter Boyle <paboyle@ph.ed.ac.uk>

    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 */
#ifndef GRID_CONJUGATE_RESIDUAL_H
#define GRID_CONJUGATE_RESIDUAL_H

NAMESPACE_BEGIN(Grid);

/////////////////////////////////////////////////////////////
// Base classes for iterative processes based on operators
// single input vec, single output vec.
/////////////////////////////////////////////////////////////

template<class Field> 
class ConjugateResidual : public OperatorFunction<Field> {
public:                                                
  RealD   Tolerance;
  Integer MaxIterations;
  int verbose;

  ConjugateResidual(RealD tol,Integer maxit) : Tolerance(tol), MaxIterations(maxit) { 
    verbose=0;
  };

  void operator() (LinearOperatorBase<Field> &Linop,const Field &src, Field &psi){

    RealD a, b, c, d;
    RealD cp, ssq,rsq;
      
    RealD rAr, rAAr, rArp;
    RealD pAp, pAAp;

    GridBase *grid = src._grid;
    psi=zero;
    Field r(grid),  p(grid), Ap(grid), Ar(grid);
      
    r=src;
    p=src;

    Linop.HermOpAndNorm(p,Ap,pAp,pAAp);
    Linop.HermOpAndNorm(r,Ar,rAr,rAAr);

    cp =norm2(r);
    ssq=norm2(src);
    rsq=Tolerance*Tolerance*ssq;

    if (verbose) std::cout<<GridLogMessage<<"ConjugateResidual: iteration " <<0<<" residual "<<cp<< " target"<< rsq<<std::endl;

    for(int k=1;k<MaxIterations;k++){

      a = rAr/pAAp;

      axpy(psi,a,p,psi);

      cp = axpy_norm(r,-a,Ap,r);

      rArp=rAr;

      Linop.HermOpAndNorm(r,Ar,rAr,rAAr);

      b   =rAr/rArp;
 
      axpy(p,b,p,r);
      pAAp=axpy_norm(Ap,b,Ap,Ar);
	
      if(verbose) std::cout<<GridLogMessage<<"ConjugateResidual: iteration " <<k<<" residual "<<cp<< " target"<< rsq<<std::endl;

      if(cp<rsq) {
	Linop.HermOp(psi,Ap);
	axpy(r,-1.0,src,Ap);
	RealD true_resid = norm2(r)/ssq;
	std::cout<<GridLogMessage<<"ConjugateResidual: Converged on iteration " <<k
		 << " computed residual "<<sqrt(cp/ssq)
		 << " true residual "<<sqrt(true_resid)
		 << " target "       <<Tolerance <<std::endl;
	return;
      }

    }

    std::cout<<GridLogMessage<<"ConjugateResidual did NOT converge"<<std::endl;
    assert(0);
  }
};
NAMESPACE_END(Grid);
#endif