added: stopping criterion in time stepping

this allows to stop the time stepping based on
some kind of application-defined norm. e.g.
when the norm of increments between timesteps falls
below some threshold

src/SIM/TimeStep.C

@@ -32,6 +32,8 @@ TimeStep::TimeStep () : step(0), iter(time.it), lstep(0)
   f1 = 1.5;
   f2 = 0.25;
   maxStep = niter = 0;
+  stop_tol = 0.0;
+  incNorm = 1.0;
   stepIt = mySteps.end();
 }
 
@@ -51,6 +53,8 @@ TimeStep& TimeStep::operator= (const TimeStep& ts)
   maxStep = ts.maxStep;
   niter = ts.niter;
   iter = ts.iter;
+  stop_tol = ts.stop_tol;
+  incNorm = ts.incNorm;
 
   time = ts.time;
   mySteps = ts.mySteps;
@@ -110,6 +114,7 @@ bool TimeStep::parse (const TiXmlElement* elem)
   utl::getAttribute(elem,"dtMax",dtMax);
   utl::getAttribute(elem,"maxCFL",maxCFL);
   utl::getAttribute(elem,"nInitStep",nInitStep);
+  utl::getAttribute(elem,"stop_tolerance",stop_tol);
   utl::getAttribute(elem,"maxStep",maxStep);
   utl::getAttribute(elem,"f1",f1);
   utl::getAttribute(elem,"f2",f2);
@@ -266,6 +271,12 @@ bool TimeStep::increment ()
                << std::endl;
     return false;
   }
+  else if (incNorm < stop_tol)
+  {
+    IFEM::cout <<"\n  ** Terminating, solution increment norm "
+               << incNorm << " less than tolerance " << stop_tol << std::endl;
+    return false;
+  }
 
   niter = iter;
   time.t += time.dt;

src/SIM/TimeStep.h

@@ -76,6 +76,7 @@ class TimeStep
   double starTime; //!< Start time of simulation
   double stopTime; //!< Stop time of simulation
   double maxCFL;   //!< CFL restriction on time step size (0.0: no restriction)
+  double incNorm; //!< Norm of change between timesteps
 
 private:
   int niter;     //!< Number of iterations in previous time step
@@ -87,6 +88,8 @@ class TimeStep
   double f1;     //!< Scale factor for increased time step size
   double f2;     //!< Scale factor for reduced time step size
 
+  double stop_tol; //!< Stop time step loop if incNorm < stop_tol
+
   typedef std::pair<std::vector<double>,double> Step; //!< Time step definition
   typedef std::vector<Step> TimeSteps;                //!< Time step container