[Implicit][FluxVarVector] Add update method for a single fluxVar

dumux/implicit/fluxvariablesvector.hh

@@ -39,6 +39,7 @@ class FluxVariablesVector
     using GridView = typename GET_PROP_TYPE(TypeTag, GridView);
     using IndexType = typename GridView::IndexSet::IndexType;
     using FluxVariables = typename GET_PROP_TYPE(TypeTag, FluxVariables);
+    using SubControlVolumeFace = typename GET_PROP_TYPE(TypeTag, SubControlVolumeFace);
 
 public:
     void update(const Problem& problem)
@@ -54,6 +55,17 @@ public:
         }
     }
 
+    void update(const Problem& problem, const SubControlVolumeFace& scvFace)
+    {
+        (*this)[scvFace.index()].update(problem, scvf);
+    }
+
+    void update(const Problem& problem, const IndexType scvFaceIndex)
+    {
+        auto&& scvFace = problem.model().fvGeometries().SubControlVolumeFace(scvFaceIndex);
+        (*this)[scvFace.index()].update(problem, scvf);
+    }
+
     const FluxVariables& operator [](IndexType scvfIdx) const
     {
         return fluxVars_[scvfIdx];