WilsonGaugeAction.h

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/*************************************************************************************
 
Grid physics library, www.github.com/paboyle/Grid
 
Source file: ./lib/qcd/action/gauge/WilsonGaugeAction.h
 
Copyright (C) 2015
 
Author: Azusa Yamaguchi <ayamaguc@staffmail.ed.ac.uk>
Author: Peter Boyle <paboyle@ph.ed.ac.uk>
Author: neo <cossu@post.kek.jp>
Author: paboyle <paboyle@ph.ed.ac.uk>
Author: Guido Cossu <guido.cossu@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 QCD_WILSON_GAUGE_ACTION_H
#define QCD_WILSON_GAUGE_ACTION_H

NAMESPACE_BEGIN(Grid);

// Wilson Gauge Action .. should I template the Nc etc..
template <class Gimpl>
class WilsonGaugeAction : public Action<typename Gimpl::GaugeField>
{
public:
  INHERIT_GIMPL_TYPES(Gimpl);
 
  using Action<GaugeField>::S;
  using Action<GaugeField>::Sinitial;
  using Action<GaugeField>::deriv;
  using Action<GaugeField>::refresh;
  
  explicit WilsonGaugeAction(RealD beta_):beta(beta_){};
 
  virtual std::string action_name() {return "WilsonGaugeAction";}
 
  virtual std::string LogParameters(){
    std::stringstream sstream;
    sstream << GridLogMessage << "[WilsonGaugeAction] Beta: " << beta << std::endl;
    return sstream.str();
  }

  virtual void refresh(const GaugeField &U, GridSerialRNG &sRNG, GridParallelRNG &pRNG){};

  virtual RealD S(const GaugeField &U) {
    RealD plaq = WilsonLoops<Gimpl>::avgPlaquette(U);
    RealD vol = U.Grid()->gSites();
 
    // Comparing with Gattringer and Lang Eq. (3.93),
    // taking the _average_ plaquette here means that
    // multiplying explicitly by the volume and dimensionality factors is needed,
    // but the factor of \f$1 / N_c\f$ divides out.
    RealD action = beta * (1.0 - plaq) * (Nd * (Nd - 1.0)) * vol * 0.5;
    return action;
  };

  virtual void deriv(const GaugeField &U, GaugeField &dSdU) {
    RealD factor = 0.5 * beta / RealD(Nc);
    GridBase *grid = U.Grid();
 
    GaugeLinkField dSdU_mu(grid);
    std::vector<GaugeLinkField> Umu(Nd, grid);
    for (int mu = 0; mu < Nd; mu++) {
      Umu[mu] = PeekIndex<LorentzIndex>(U, mu);
    }
 
    for (int mu = 0; mu < Nd; mu++) {
      // Staple in direction mu
      WilsonLoops<Gimpl>::Staple(dSdU_mu, Umu, mu);
      dSdU_mu = Ta(Umu[mu] * dSdU_mu) * factor;
 
      PokeIndex<LorentzIndex>(dSdU, dSdU_mu, mu);
    }
  }
 
private:
  RealD beta;  
 };

NAMESPACE_END(Grid);
#endif