[PL] f-f_0 -> u_0 - u; fixed docu.

ProcessLib/BoundaryCondition/UniformRobinBoundaryCondition.cpp

@@ -25,14 +25,14 @@ createUniformRobinBoundaryCondition(
 
     //! \ogs_file_param{boundary_condition__UniformRobin__alpha}
     double const alpha = config.getConfigParameter<double>("alpha");
-    //! \ogs_file_param{boundary_condition__UniformRobin__f_0}
-    double const f_0 = config.getConfigParameter<double>("f_0");
+    //! \ogs_file_param{boundary_condition__UniformRobin__u_0}
+    double const u_0 = config.getConfigParameter<double>("u_0");
 
     return std::unique_ptr<UniformRobinBoundaryCondition>(
         new UniformRobinBoundaryCondition(
             integration_order, dof_table, variable_id, component_id, global_dim,
             std::move(elements),
-            UniformRobinBoundaryConditionData{alpha, f_0}));
+            UniformRobinBoundaryConditionData{alpha, u_0}));
 }
 
 }  // ProcessLib

ProcessLib/BoundaryCondition/UniformRobinBoundaryCondition.h

@@ -27,9 +27,13 @@ using UniformRobinBoundaryCondition = GenericNaturalBoundaryCondition<
 /*! Creates a new uniform Robin boundary condition from the given data.
  *
  * The Robin boundary condition is given in the form
- * \f$ \partial f/\partial n = \alpha \cdot [ f(x) - f_0 ] \f$,
- * where the coefficients \f$ \alpha \f$ and \f$ f_0 \f$ are obtained from the
- * \c config.
+ * \f$ \alpha \cdot [ u_0 - u(x) ] \f$,
+ * where the coefficients \f$ \alpha \f$ and \f$ u_0 \f$ are obtained from the
+ * \c config, and \f$ u \f$ is the unknown to which the boundary condition is
+ * applied.
+ *
+ * The value \f$ \alpha \cdot [ u_0 - u(x) ] \f$ is a flux. It replaces the
+ * integrand in the boundary integral for the variable \f$ u \f$.
  */
 std::unique_ptr<UniformRobinBoundaryCondition>
 createUniformRobinBoundaryCondition(

ProcessLib/BoundaryCondition/UniformRobinBoundaryConditionLocalAssembler.h

@@ -16,7 +16,7 @@ namespace ProcessLib
 {
 struct UniformRobinBoundaryConditionData final {
     double const alpha;
-    double const f_0;
+    double const u_0;
 };
 
 template <typename ShapeFunction, typename IntegrationMethod,
@@ -59,13 +59,13 @@ public:
             auto const& sm = Base::_shape_matrices[ip];
             auto const& wp = integration_method.getWeightedPoint(ip);
 
-            // df/dn = alpha ( f - f_0 )
-            // adding a -alpha term to the diagonal of the stiffness matrix
-            // and a -alpha * f_0 term to the rhs vector
-            _local_K.diagonal().noalias() -=
+            // flux = alpha * ( u_0 - u )
+            // adding a alpha term to the diagonal of the stiffness matrix
+            // and a alpha * u_0 term to the rhs vector
+            _local_K.diagonal().noalias() +=
                 sm.N * _data.alpha * sm.detJ * wp.getWeight();
-            _local_rhs.noalias() -=
-                sm.N * _data.alpha * _data.f_0 * sm.detJ * wp.getWeight();
+            _local_rhs.noalias() +=
+                sm.N * _data.alpha * _data.u_0 * sm.detJ * wp.getWeight();
         }
 
         auto const indices = NumLib::getIndices(id, dof_table_boundary);