distinguish between the number of non linear iterations and the number of linearizations

while the printed number of "Non linear iterations" was correct in a
strict sense, it was very confusing if one was working on the
linearization code because the last Newton iteration of each time step
was linearized but not solved for (and the solution was thus not
updated hence it does not count as a "non linear iteration"). This
makes sense for large problems were the total runtime is completely
dominated by the performance of the linear solver, but smaller
problems exhibit the opposite behavior (i.e., for them, runtime is
typically dominated by the linearization proceedure), so one is more
interested in the number of linearizations, not the number of linear
solves.

opm/autodiff/NonlinearSolver_impl.hpp

@@ -32,6 +32,7 @@ namespace Opm
                                                     std::unique_ptr<PhysicalModel> model_arg)
         : param_(param),
           model_(std::move(model_arg)),
+          linearizations_(0),
           nonlinearIterations_(0),
           linearIterations_(0),
           wellIterations_(0),
@@ -44,6 +45,12 @@ namespace Opm
         }
     }
 
+    template <class PhysicalModel>
+    int NonlinearSolver<PhysicalModel>::linearizations() const
+    {
+        return linearizations_;
+    }
+
     template <class PhysicalModel>
     int NonlinearSolver<PhysicalModel>::nonlinearIterations() const
     {
@@ -149,6 +156,7 @@ namespace Opm
 
         linearIterations_ += linIters;
         nonlinearIterations_ += iteration - 1; // Since the last one will always be trivial.
+        linearizations_ += iteration;
         wellIterations_ += wellIters;
         linearIterationsLast_ = linIters;
         nonlinearIterationsLast_ = iteration;