Add non-const overload of model().

opm/autodiff/NonlinearSolver.hpp

@@ -100,6 +100,9 @@ namespace Opm {
         /// Reference to physical model.
         const PhysicalModel& model() const;
 
+        /// Mutable reference to physical model.
+        PhysicalModel& model();
+
         /// Detect oscillation or stagnation in a given residual history.
         void detectOscillations(const std::vector<std::vector<double>>& residual_history,
                                 const int it, bool& oscillate, bool& stagnate) const;

opm/autodiff/NonlinearSolver_impl.hpp

@@ -60,6 +60,12 @@ namespace Opm
         return *model_;
     }
 
+    template <class PhysicalModel>
+    PhysicalModel& NonlinearSolver<PhysicalModel>::model()
+    {
+        return *model_;
+    }
+
     template <class PhysicalModel>
     unsigned int NonlinearSolver<PhysicalModel>::nonlinearIterationsLastStep() const
     {