Merge branch 'feature/sum-energy' into 'master'

SumEnergy: Allow more than two local energies

See merge request !34

dune/elasticity/materials/sumenergy.hh

 #ifndef DUNE_ELASTICITY_MATERIALS_SUMENERGY_HH
 #define DUNE_ELASTICITY_MATERIALS_SUMENERGY_HH
 
+#include <vector>
+
 #include <dune/common/fmatrix.hh>
 #include <dune/common/fmatrixev.hh>
 
@@ -24,26 +26,38 @@ class SumEnergy
 
 public:
 
-  /** \brief Constructor with a set of material parameters
-   * \param parameters The material parameters
-   */
+  /** \brief Constructor with two local energies (compatibility for old interface)*/
   SumEnergy(std::shared_ptr<Elasticity::LocalEnergy<LocalView, field_type>> a,
             std::shared_ptr<Elasticity::LocalEnergy<LocalView, field_type>> b)
-  : a_(a),
-    b_(b)
+  {
+    addLocalEnergy(a);
+    addLocalEnergy(b);
+  }
+
+  /** \brief Default Constructor*/
+  SumEnergy()
   {}
 
+  /** \brief Add a local energy to be part of the sum */
+  void addLocalEnergy( std::shared_ptr<Elasticity::LocalEnergy<LocalView, field_type>> localEnergy )
+  {
+    localEnergies_.push_back(localEnergy);
+  }
+
   /** \brief Assemble the energy for a single element */
   field_type energy (const LocalView& localView,
                      const std::vector<field_type>& localConfiguration) const
   {
-    return a_->energy(localView, localConfiguration)
-         + b_->energy(localView, localConfiguration);
+    field_type sum = 0.;
+    for ( const auto& localEnergy : localEnergies_ )
+      sum += localEnergy->energy( localView, localConfiguration );
+
+    return sum;
   }
 
 private:
-  std::shared_ptr<Elasticity::LocalEnergy<LocalView, field_type>> a_;
-  std::shared_ptr<Elasticity::LocalEnergy<LocalView, field_type>> b_;
+  // vector containing pointers to the local energies
+  std::vector<std::shared_ptr<Elasticity::LocalEnergy<LocalView, field_type>>> localEnergies_;
 };
 
 }  // namespace Dune::Elasticity