From 453cf2a1c630ed8fc164858c9f8a483e40255673 Mon Sep 17 00:00:00 2001
From: Guido Cossu <guido.cossu@ed.ac.uk>
Date: Tue, 2 May 2017 14:40:12 +0100
Subject: [PATCH] Moving the topological charge outside the HMC related
 routines

---
 lib/qcd/observables/topological_charge.h | 19 +------------------
 lib/qcd/utils/WilsonLoops.h              | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 18 deletions(-)

diff --git a/lib/qcd/observables/topological_charge.h b/lib/qcd/observables/topological_charge.h
index 6188b9e8..5d09c420 100644
--- a/lib/qcd/observables/topological_charge.h
+++ b/lib/qcd/observables/topological_charge.h
@@ -49,24 +49,7 @@ class TopologicalCharge : public HmcObservable<typename Impl::Field> {
                             GridSerialRNG &sRNG,
                             GridParallelRNG &pRNG) {
 
-    // 4d topological charge
-    // Bx = -iF(y,z), By = -iF(z,y), Bz = -iF(x,y)
-    GaugeLinkField Bx(U._grid), By(U._grid), Bz(U._grid);
-    WilsonLoops<Impl>::FieldStrength(Bx, U, Ydir, Zdir);
-    WilsonLoops<Impl>::FieldStrength(By, U, Zdir, Xdir);
-    WilsonLoops<Impl>::FieldStrength(Bz, U, Xdir, Ydir);
-
-    // Ex = -iF(t,x), Ey = -iF(t,y), Ez = -iF(t,z)
-    GaugeLinkField Ex(U._grid), Ey(U._grid), Ez(U._grid);
-    WilsonLoops<Impl>::FieldStrength(Ex, U, Tdir, Xdir);
-    WilsonLoops<Impl>::FieldStrength(Ey, U, Tdir, Ydir);
-    WilsonLoops<Impl>::FieldStrength(Ez, U, Tdir, Zdir);
-
-    double coeff = 8.0/(32.0*M_PI*M_PI);
-
-    LatticeComplex qfield = coeff*trace(Bx*Ex + By*Ey + Bz*Ez);
-    TComplex Tq = sum(qfield);
-    Real q = TensorRemove(Tq).real();
+    Real q = WilsonLoops<Impl>::TopologicalCharge(U);
 
     int def_prec = std::cout.precision();
 
diff --git a/lib/qcd/utils/WilsonLoops.h b/lib/qcd/utils/WilsonLoops.h
index c2edb145..5382882e 100644
--- a/lib/qcd/utils/WilsonLoops.h
+++ b/lib/qcd/utils/WilsonLoops.h
@@ -313,6 +313,27 @@ public:
       FS = 0.25*Ta(u*v + Cshift(vu, mu, +1));
   }
 
+  static Real TopologicalCharge(GaugeLorentz &U){
+    // 4d topological charge
+    assert(Nd==4);
+    // Bx = -iF(y,z), By = -iF(z,y), Bz = -iF(x,y)
+    GaugeMat Bx(U._grid), By(U._grid), Bz(U._grid);
+    FieldStrength(Bx, U, Ydir, Zdir);
+    FieldStrength(By, U, Zdir, Xdir);
+    FieldStrength(Bz, U, Xdir, Ydir);
+
+    // Ex = -iF(t,x), Ey = -iF(t,y), Ez = -iF(t,z)
+    GaugeMat Ex(U._grid), Ey(U._grid), Ez(U._grid);
+    FieldStrength(Ex, U, Tdir, Xdir);
+    FieldStrength(Ey, U, Tdir, Ydir);
+    FieldStrength(Ez, U, Tdir, Zdir);
+
+    double coeff = 8.0/(32.0*M_PI*M_PI);
+
+    LatticeComplex qfield = coeff*trace(Bx*Ex + By*Ey + Bz*Ez);
+    TComplex Tq = sum(qfield);
+    return TensorRemove(Tq).real();
+  }
 
   //////////////////////////////////////////////////////
   // Similar to above for rectangle is required