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+/*  This file is part of the OpenLB library
+ *
+ *  Copyright (C) 2018 Adrian Kummerlaender
+ *  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.
+*/
+
+#ifndef FUNCTOR_DSL_3D_H
+#define FUNCTOR_DSL_3D_H
+
+#include "functors/lattice/superBaseF3D.h"
+#include "functors/lattice/indicator/superIndicatorF3D.h"
+#include "functors/analytical/analyticalBaseF.h"
+
+namespace olb {
+
+/// Helper functions for building functors via composition
+/**
+ * Certain types of functors such as error norms (see e.g. SuperRelativeErrorLpNorm3D)
+ * lend themselves to being expressed as a composition of existing functors.
+ *
+ * std::shared_ptr based functor arithmetic offers a memory-safe way to perform
+ * functor composition. However common operations such as lifting stack-allocated
+ * functors into the std::shared_ptr context, constructing Lp norms or restricting
+ * analytical functors on a lattice can become quite verbose.
+ *
+ * This is why the `functor_dsl` namespace contains a set of conveniently named
+ * helper functions that aim to ease writing composed functors.
+ *
+ * e.g. a slightly modified version of SuperRelativeErrorLpNorm3D's constructor:
+ *
+ * \code{.cpp}
+ * using namespace functor_dsl;
+ *
+ * // decltype(wantedF)    == std::shared_ptr<AnalyticalF3D<T,W>>
+ * // decltype(f)          == std::shared_ptr<SuperF3D<T,W>>
+ * // decltype(indicatorF) == std::shared_ptr<SuperIndicatorF3D<T>>
+ *
+ * auto wantedLatticeF = restrict(wantedF, sLattice);
+ * auto relaticeErrorF = norm<P>(wantedLatticeF - f, indicatorF)
+ *                     / norm<P>(wantedLatticeF, indicatorF);
+ * \endcode
+ *
+ * Note that any of the functors managed by std::shared_ptr may be returned
+ * and reused independently.
+ *
+ * i.e. it is not necessary to manually assure the lifetime of any functor
+ * used by the composition.
+ **/
+namespace functor_dsl {
+
+/// Lifts functor reference to std::shared_ptr functor arithmetic
+template<typename T, typename W>
+std::shared_ptr<SuperF3D<T,W>> lift(SuperF3D<T,W>& f);
+
+/// Lifts functor pointer to std::shared_ptr functor arithmetic
+template<typename T, typename W>
+std::shared_ptr<SuperF3D<T,W>> lift(SuperF3D<T,W>* f);
+
+/// Lifts functor reference to std::shared_ptr functor arithmetic
+template<typename T, typename S>
+std::shared_ptr<AnalyticalF3D<T,S>> lift(AnalyticalF3D<T,S>& f);
+
+/// Lifts functor pointer to std::shared_ptr functor arithmetic
+template<typename T, typename W>
+std::shared_ptr<AnalyticalF3D<T,S>> lift(AnalyticalF3D<T,S>* f);
+
+/// Returns baseF raised to the power of exponentF
+template<typename T, typename W>
+std::shared_ptr<SuperF3D<T,W>> pow(std::shared_ptr<SuperF3D<T,W>> baseF,
+                                   std::shared_ptr<SuperF3D<T,W>> exponentF);
+
+/// Returns baseF raised to the power of exponent
+template<typename T, typename W, typename E>
+std::shared_ptr<SuperF3D<T,W>> pow(std::shared_ptr<SuperF3D<T,W>> baseF,
+                                   E exponent);
+
+/// Returns base raised to the power of exponentF
+template<typename T, typename W, typename B>
+std::shared_ptr<SuperF3D<T,W>> pow(B base,
+                                   std::shared_ptr<SuperF3D<T,W>> exponentF);
+
+/// Returns Lp norm for a functor f on the subset described by indicatorF
+template<int P, typename T, typename W>
+std::shared_ptr<SuperF3D<T,W>> norm(std::shared_ptr<SuperF3D<T,W>>        f,
+                                    std::shared_ptr<SuperIndicatorF3D<T>> indicatorF);
+
+/// Returns restriction of a analytical functor f to the lattice sLattice
+template<typename T, typename W, typename DESCRIPTOR>
+std::shared_ptr<SuperF3D<T,W>> restrict(std::shared_ptr<AnalyticalF3D<T,W>> f,
+                                        SuperLattice3D<T, DESCRIPTOR>& sLattice);
+
+}
+
+}
+
+#endif