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+/*  This file is part of the OpenLB library
+ *
+ *  Copyright (C) 2008 Jonas Latt
+ *  E-mail contact: info@openlb.net
+ *  The most recent release of OpenLB can be downloaded at
+ *  <http://www.openlb.net/>
+ *
+ *  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.
+*/
+
+/** \file
+ * BGK Dynamics with adjustable speed of sound -- generic implementation.
+ */
+#ifndef CHOPARD_DYNAMICS_HH
+#define CHOPARD_DYNAMICS_HH
+
+#include "chopardDynamics.h"
+#include "core/util.h"
+
+namespace olb {
+
+////////////////////// Class ChopardDynamics //////////////////////////
+
+/** \param vs2_ speed of sound
+ *  \param momenta_ a Momenta object to know how to compute velocity momenta
+ *  \param momenta_ a Momenta object to know how to compute velocity momenta
+ */
+template<typename T, typename DESCRIPTOR>
+ChopardDynamics<T,DESCRIPTOR>::ChopardDynamics (
+  T vs2_, T omega_, Momenta<T,DESCRIPTOR>& momenta_ )
+  : BasicDynamics<T,DESCRIPTOR>(momenta_),
+    vs2(vs2_),
+    omega(omega_)
+{ }
+
+/** With this constructor, the speed of sound is vs2 = cs2
+ *  \param omega_ relaxation parameter, related to the dynamic viscosity
+ *  \param momenta_ a Momenta object to know how to compute velocity momenta
+ */
+template<typename T, typename DESCRIPTOR>
+ChopardDynamics<T,DESCRIPTOR>::ChopardDynamics (
+  T omega_, Momenta<T,DESCRIPTOR>& momenta_ )
+  : BasicDynamics<T,DESCRIPTOR>(momenta_),
+    vs2((T)1/descriptors::invCs2<T,DESCRIPTOR>()),
+    omega(omega_)
+{ }
+
+template<typename T, typename DESCRIPTOR>
+T ChopardDynamics<T,DESCRIPTOR>::computeEquilibrium
+(int iPop, T rho, const T u[DESCRIPTOR::d], T uSqr) const
+{
+  return chopardEquilibrium(iPop, rho, u, uSqr, vs2);
+}
+
+template<typename T, typename DESCRIPTOR>
+void ChopardDynamics<T,DESCRIPTOR>::collide (
+  Cell<T,DESCRIPTOR>& cell,
+  LatticeStatistics<T>& statistics )
+{
+  T rho, u[DESCRIPTOR::d];
+  this->_momenta.computeRhoU(cell, rho, u);
+  T uSqr = chopardBgkCollision(cell, rho, u, vs2, omega);
+  statistics.incrementStats(rho, uSqr);
+}
+
+template<typename T, typename DESCRIPTOR>
+T ChopardDynamics<T,DESCRIPTOR>::getOmega() const
+{
+  return omega;
+}
+
+template<typename T, typename DESCRIPTOR>
+void ChopardDynamics<T,DESCRIPTOR>::setOmega(T omega_)
+{
+  omega = omega_;
+}
+
+template<typename T, typename DESCRIPTOR>
+T ChopardDynamics<T,DESCRIPTOR>::getVs2() const
+{
+  return vs2;
+}
+
+template<typename T, typename DESCRIPTOR>
+void ChopardDynamics<T,DESCRIPTOR>::setVs2(T vs2_)
+{
+  vs2 = vs2_;
+}
+
+template<typename T, typename DESCRIPTOR>
+T ChopardDynamics<T,DESCRIPTOR>::chopardBgkCollision (
+  Cell<T,DESCRIPTOR>& cell, T rho, const T u[DESCRIPTOR::d], T vs2, T omega)
+{
+  const T uSqr = util::normSqr<T,DESCRIPTOR::d>(u);
+  for (int iPop=0; iPop < DESCRIPTOR::q; ++iPop) {
+    cell[iPop] *= (T)1-omega;
+    cell[iPop] += omega * chopardEquilibrium(iPop, rho, u, uSqr, vs2);
+  }
+  return uSqr;
+}
+
+template<typename T, typename DESCRIPTOR>
+T ChopardDynamics<T,DESCRIPTOR>::chopardEquilibrium (
+  int iPop, T rho, const T u[DESCRIPTOR::d], T uSqr, T vs2)
+{
+  if (iPop==0) {
+    return rho*( (T)1 -
+                 vs2*descriptors::invCs2<T,DESCRIPTOR>()*((T)1-descriptors::t<T,DESCRIPTOR>(0)) -
+                 descriptors::t<T,DESCRIPTOR>(0)/(T)2*descriptors::invCs2<T,DESCRIPTOR>()*uSqr ) - descriptors::t<T,DESCRIPTOR>(0);
+  } else {
+    T c_u = T();
+    for (int iD=0; iD < DESCRIPTOR::d; ++iD) {
+      c_u += descriptors::c<DESCRIPTOR>(iPop,iD)*u[iD];
+    }
+    return rho * descriptors::t<T,DESCRIPTOR>(iPop) * descriptors::invCs2<T,DESCRIPTOR>()* (
+             vs2 + c_u +
+             descriptors::invCs2<T,DESCRIPTOR>() / (T)2 * c_u*c_u -
+             uSqr / (T)2
+           ) - descriptors::t<T,DESCRIPTOR>(iPop);
+  }
+}
+
+
+}
+
+#endif