Finish the implementation of the 'gradient' method

No real way to test it though, yet.

dune/fracture-phasefields/elasticenergyfunctional.hh

@@ -485,24 +485,18 @@ public:
 
   Vector gradient(const Vector& v)
   {
-    typedef typename Vector::block_type LocalGradientVector;
-    // TODO: I don't really know what to replace the '3' with
-    typedef typename Dune::FieldVector<double, 3> FunctionalGradient;
-
     Vector result;
-    LocalGradientVector BiXv;
-    FunctionalGradient Dgamma;
+    Solvers::resizeInitializeZero(result,v);
+
+    typename LocalEnergy::Domain BiXv;
 
     for (std::size_t i=0; i<evaluationMatrix().N(); ++i)
     {
       BiXv  = 0.0;
       addRowXVector(evaluationMatrix()[i], v, BiXv);
 
-      // TODO: What happens to the 'variants' in the following line stolen from couplednonlinearity.hh?
-      // Dgamma = gamma_[i % variants]->d(BiXv);
       auto localEnergyDerivative = derivative(localEnergy());
-      // TODO: The following line does not compile -- I must be getting one of the types wrong
-      //Dgamma = localEnergyDerivative(BiXv);
+      auto Dgamma = localEnergyDerivative(BiXv);
       Dgamma *= (*weightVector_)[i];
 
       addRowTransposedXVector(evaluationMatrix()[i], Dgamma, result);
@@ -516,7 +510,7 @@ protected:
 
   static void addRowXVector(const typename EvaluationMatrix::row_type& evaluationMatrixRow,
                             const Vector& x,
-                            typename Vector::block_type& y)
+                            typename LocalEnergy::Domain& y)
   {
     auto it  = evaluationMatrixRow.begin();
     auto end = evaluationMatrixRow.end();
@@ -525,7 +519,7 @@ protected:
   }
 
   static void addRowTransposedXVector(const typename EvaluationMatrix::row_type& evaluationMatrixRow,
-                                      const Dune::FieldVector<double,3>& x,
+                                      const typename LocalEnergy::Domain& x,  // Actually: the range of the gradient
                                       Vector& y)
   {
     auto it  = evaluationMatrixRow.begin();