/Users/mdipierro/fermiqcd/development/Libraries/fermiqcd_minres_inverter.h

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class inversion_stats {
 public:
  mdp_real target_absolute_precision;
  mdp_real target_relative_precision;
  int      max_steps;
  mdp_real residue;
  mdp_real absolute_precision;
  mdp_real relative_precision;
  int      steps;
  int      mul_Q_steps;
  mdp_real time;
};

// /////////////////////////////////////////////
// implementation of the minimum residue inversion
// /////////////////////////////////////////////

class MinRes {
 public:
  template <class fieldT, class fieldG>
  static inversion_stats inverter(fieldT &psi_out, 
                                  fieldT &psi_in, 
                                  fieldG &U, 
                                  coefficients &coeff, 
                                  mdp_real absolute_precision=mdp_precision,
                                  mdp_real relative_precision=0,
                                  int max_steps=2000) {
    
    mpi.begin_function("MinimumResidueInverter");
    
    fieldT          q(psi_in);
    fieldT          r(psi_in);
    double          residue, rresidue=-1, old_rresidue;
    mdp_complex         alpha;
    mdp_int            step=0;
    double          time=mpi.time();
    inversion_stats stats;
    
    psi_in.update();
    mul_Q(r,psi_in,U,coeff);
    r*=-1;
    r+=psi_in;
    psi_out=psi_in;
    
    mpi << "\t<target>\n" 
        << "\t\t<max_steps>" << max_steps << "</max_steps>\n"
        << "\t\t<absolute_precision>" << absolute_precision << "</absolute_precision>\n"
        << "\t\t<relative_precision>" << relative_precision << "</relative_precision>\n"
        << "\t</target>\n";
    
    do {
      r.update();
      mul_Q(q,r,U,coeff);
      alpha=q*r;
      alpha/=norm_square(q);
      mdp_add_scaled_field(psi_out, alpha, r);
      mdp_add_scaled_field(r, -alpha, q);
      
      // computing residue
      residue=norm_square(r);
      residue=sqrt(residue/r.global_size());
      
      // computing relative residue
      old_rresidue=rresidue;
      rresidue=relative_residue(r,psi_out);
      
      mpi << "\t\t<step>" << step << "</step>\n"
          << "\t\t<residue>" << residue << "</residue>\n"
          << "\t\t<relative_residue>" << rresidue << "</relative_residue>\n"
          << "\t\t<time>" << mpi.time()-time << "</time>\n\n";
      
      if((step>10) && (rresidue==old_rresidue))
        error("not converging"); 
      step++;
    } while (residue>absolute_precision &&
             rresidue>relative_precision &&
             step<max_steps);
    
    psi_out.update();
    
    stats.target_absolute_precision=absolute_precision;
    stats.target_relative_precision=relative_precision;
    stats.max_steps=max_steps;
    stats.absolute_precision=residue;
    stats.relative_precision=rresidue;
    stats.residue=residue;
    stats.steps=step;
    stats.mul_Q_steps=step+1;
    stats.time=mpi.time()-time;
    
    mpi << "\t<stats>\n" 
        << "\t\t<max_steps>" << step << "</max_steps>\n"
        << "\t\t<absolute_precision>" << residue << "</absolute_precision>\n"
        << "\t\t<relative_precision>" << rresidue << "</relative_precision>\n"
        << "\t\t<time>" << stats.time << "</time>\n"
        << "\t</stats>\n";
    
    mpi.end_function("MinimumResidueInverter");
    return stats;
  }
};

template <class fieldT, class fieldG>
inversion_stats MinimumResidueInverter(fieldT &psi_out, 
                                       fieldT &psi_in, 
                                       fieldG &U, 
                                       coefficients &coeff, 
                                       mdp_real absolute_precision=mdp_precision,
                                       mdp_real relative_precision=0,
                                       int max_steps=2000) {
  return MinRes::inverter(psi_out,psi_in,U,coeff,
                          absolute_precision,
                          relative_precision,
                          max_steps);
}

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