added polyakov loop observable to the hmc

lib/qcd/observables/hmc_observable.h

@@ -45,5 +45,7 @@ class HmcObservable {
 
 #include "plaquette.h"
 #include "topological_charge.h"
+#include "polyakov_loop.h"
+
 
 #endif  //  HMC_OBSERVABLE_H

lib/qcd/observables/polyakov_loop.h

@@ -0,0 +1,68 @@
+/*************************************************************************************
+
+Grid physics library, www.github.com/paboyle/Grid
+
+Source file: ./lib/qcd/modules/polyakov_line.h
+
+Copyright (C) 2017
+
+Author: David Preti <david.preti@csic.es>
+
+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 HMC_POLYAKOV_H
+#define HMC_POLYAKOV_H
+
+namespace Grid {
+namespace QCD {
+
+// this is only defined for a gauge theory
+template <class Impl>
+class PolyakovLogger : public HmcObservable<typename Impl::Field> {
+ public:
+  // here forces the Impl to be of gauge fields
+  // if not the compiler will complain
+  INHERIT_GIMPL_TYPES(Impl);
+
+  // necessary for HmcObservable compatibility
+  typedef typename Impl::Field Field;
+
+  void TrajectoryComplete(int traj,
+                          Field &U,
+                          GridSerialRNG &sRNG,
+                          GridParallelRNG &pRNG) {
+
+    ComplexD polyakov = WilsonLoops<Impl>::avgPolyakovLoop(U);
+
+    int def_prec = std::cout.precision();
+
+    std::cout << GridLogMessage
+        << std::setprecision(std::numeric_limits<Real>::digits10 + 1)
+        << "Polyakov Loop: [ " << traj << " ] "<< polyakov << std::endl;
+
+    std::cout.precision(def_prec);
+
+  }
+};
+
+}  // namespace QCD
+}  // namespace Grid
+
+#endif  // HMC_POLYAKOV_H