Local energy densities: parameter are always `double`

This improves the automatic differentiation a bit.

dune/elasticity/materials/exphenckydensity.hh

@@ -85,7 +85,7 @@ public:
   }
 
   /** \brief Lame constants */
-  field_type mu_, lambda_, kappa_, k_, khat_, alpha_, beta_;
+  double mu_, lambda_, kappa_, k_, khat_, alpha_, beta_;
 };
 
 } // namespace Dune::Elasticity

dune/elasticity/materials/mooneyrivlindensity.hh

@@ -126,19 +126,19 @@ public:
   }
 
   /** \brief Lame constants */
-  field_type mooneyrivlin_a,
-             mooneyrivlin_b,
-             mooneyrivlin_c,
-             mooneyrivlin_10,
-             mooneyrivlin_01,
-             mooneyrivlin_20,
-             mooneyrivlin_02,
-             mooneyrivlin_11,
-             mooneyrivlin_30,
-             mooneyrivlin_21,
-             mooneyrivlin_12,
-             mooneyrivlin_03,
-             mooneyrivlin_k;
+  double mooneyrivlin_a,
+         mooneyrivlin_b,
+         mooneyrivlin_c,
+         mooneyrivlin_10,
+         mooneyrivlin_01,
+         mooneyrivlin_20,
+         mooneyrivlin_02,
+         mooneyrivlin_11,
+         mooneyrivlin_30,
+         mooneyrivlin_21,
+         mooneyrivlin_12,
+         mooneyrivlin_03,
+         mooneyrivlin_k;
   std::string mooneyrivlin_energy;
 };
 

dune/elasticity/materials/neohookedensity.hh

@@ -76,7 +76,7 @@ public:
   }
 
   /** \brief Lame constants */
-  field_type mu_, lambda_, kappa_;
+  double mu_, lambda_, kappa_;
 };
 
 } // namespace Dune::Elasticity