Merge branch 'develop' into feature/gpu-port

tests/forces/Test_wilson_force.cc

@@ -170,6 +170,13 @@ int main (int argc, char ** argv)
     // Update PF action density
     dS = dS+trace(mommu*forcemu)*dt;
 
+    // Smom = - P^2 ;
+    //  dSmom = trace ( (mom+f/2dt)(mom+f/2dt) ) - trace mom*mom
+    //        = trace(mom*f) dt  + 0.25*dt*dt * trace(f*f).
+    //
+    // can we improve on this in HMC???
+    //
+    // 
     dSmom  = dSmom  - trace(mommu*forcemu) * dt;
     dSmom2 = dSmom2 - trace(forcemu*forcemu) *(0.25* dt*dt);