[linear] add norm to base class

dumux/linear/solver.hh

@@ -24,7 +24,9 @@
 #ifndef DUMUX_LINEAR_SOLVER_HH
 #define DUMUX_LINEAR_SOLVER_HH
 
+#include <dune/common/parallel/mpihelper.hh>
 #include <dune/common/exceptions.hh>
+#include <dune/istl/scalarproducts.hh>
 #include <dumux/common/parameters.hh>
 
 namespace Dumux {
@@ -71,6 +73,15 @@ public:
         DUNE_THROW(Dune::NotImplemented, "Linear solver doesn't implement a solve method!");
     }
 
+    template<class Vector>
+    auto norm(const Vector& x) const
+    {
+        if (Dune::MPIHelper::getCommunication().size() > 1)
+            DUNE_THROW(Dune::NotImplemented, "norm in parallel");
+
+        return Dune::SeqScalarProduct<Vector>().norm(x);
+    }
+
     //! the name of the linear solver
     std::string name() const
     { return "unknown solver"; }