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

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class BiCGStabVtk {
 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("BiConugateGradientStabilizedInverter");
    const string filename_prefix="test";
    const int tc=0;
    string filename1, filename2;
    int             step=0;
    fieldT          p(psi_in);
    fieldT          q(psi_in);
    fieldT          r(psi_in);
    fieldT          s(psi_in);
    fieldT          t(psi_in);
    
    mdp_field<float> sv(psi_in.lattice());
    mdp_site x(psi_in.lattice());
    double          residue, rresidue=-1, old_rresidue;
    mdp_complex         alpha, beta, rho, rho_old, omega;
    double          time=mpi.time();
    inversion_stats stats;
    
    mpi << "\tstep\tresidue\t\ttime (sec)\n";
    
    // Initial conditions
    if(BiCGStabRestart==false) 
      psi_out=psi_in; // first guess and a stupid guess!

    psi_out.update();
    mul_Q(r,psi_out,U,coeff);
    r*=-1;
    r+=psi_in;
    q=r;
    
    p=0.0;
    s=0.0;
    
    rho_old=alpha=omega=1;

    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 {
      
      rho=q*r;
      beta=(rho/rho_old)*(alpha/omega);
      rho_old=rho;
      p*=beta;
      p+=r;
      mdp_add_scaled_field(p, -beta*omega, s);
      p.update();
      mul_Q(s,p,U,coeff);
      alpha=rho/(q*s);
      mdp_add_scaled_field(r, -alpha, s);
      r.update();
      mul_Q(t,r,U,coeff);
      omega=t*r;
      omega/=norm_square(t);
      mdp_add_scaled_field(psi_out, omega, r);
      mdp_add_scaled_field(psi_out, alpha, p);

      // computation of residue
      residue=norm_square(r);
      residue=sqrt(residue/r.global_size());

      // computation of rresidue
      old_rresidue=rresidue;
      rresidue=relative_residue(r,psi_out);

      // make VTK files                                                                  
      forallsites(x) {
        sv(x)=0.0;
        for(int a=0; a<4; a++)
          for(int k=0; k<psi_in.nc; k++)
            sv(x)+=sqrt(real(psi_out(x,a,k)*conj(psi_out(x,a,k))));
      }
      filename1=filename_prefix+".field."+tostring(step)+".vtk";
      sv.save_vtk(filename1,tc);
      forallsites(x) {
        sv(x)=0.0;
        for(int a=0; a<4; a++)
          for(int k=0; k<psi_in.nc; k++)
            sv(x)+=log(real(r(x,a,k)*conj(r(x,a,k)))+PRECISION);
      }
      filename2=filename_prefix+".residue."+tostring(step)+".vtk";
      sv.save_vtk(filename2,tc);


      mdp_add_scaled_field(r, -omega, t);
      
      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=2*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("BiConugateGradientStabilizedInverter");
    return stats;
  }
};

template <class fieldT, class fieldG>
   inversion_stats BiConjugateGradientStabilizedInverterVtk(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 BiCGStabVtk::inverter(psi_out,psi_in,U,coeff,
                            absolute_precision, 
                            relative_precision,
                            max_steps);
}

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