Introduce LinearSolver interface class

A LinearSolver is a solver for a linear system of equations.
In particular, LinearSolver objects can be given a matrix
and a right-hand-side vector.

dune/solvers/solvers/CMakeLists.txt

@@ -3,6 +3,7 @@ install(FILES
     iterativesolver.cc
     iterativesolver.hh
     linearipopt.hh
+    linearsolver.hh
     loopsolver.cc
     loopsolver.hh
     quadraticipopt.hh

dune/solvers/solvers/linearsolver.hh

+// -*- tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+// vi: set et ts=8 sw=4 sts=4:
+#ifndef DUNE_SOLVERS_SOLVERS_LINEARSOLVER_HH
+#define DUNE_SOLVERS_SOLVERS_LINEARSOLVER_HH
+
+#include <dune/solvers/solvers/solver.hh>
+
+namespace Dune {
+
+namespace Solvers {
+
+/** \brief Abstract base class for solvers that solve linear problems
+ *
+ * Linear problems are problems that involve a fixed matrix and a right-hand-side
+ * vector.  Additional constraints are allowed.
+ */
+template <class Matrix, class Vector>
+class LinearSolver : public Solver
+{
+public:
+  /** \brief Constructor taking all relevant data */
+  LinearSolver(VerbosityMode verbosity)
+  : Solver(verbosity)
+  {}
+
+  /** \brief Set up the linear problem to solve */
+  virtual void setProblem(const Matrix& matrix,
+                          Vector& x,
+                          const Vector& rhs) = 0;
+
+};
+
+}   // namespace Solvers
+
+}   // namespace Dune
+
+#endif