H(|.|) can be regular at zero

dune/tectonic/localnonlinearity.hh

@@ -27,7 +27,7 @@ template <int dimension> class LocalNonlinearity {
   }
 
   double regularity(VectorType const &x) const {
-    if (x.two_norm() < 1e-8) // TODO
+    if (!func_->smoothesNorm() && x.two_norm() < 1e-12) // TODO
       return std::numeric_limits<double>::infinity();
 
     return func_->regularity(x.two_norm());

dune/tectonic/nicefunction.hh

@@ -23,6 +23,9 @@ class NiceFunction : public VirtualFunction<double, double> {
   double virtual regularity(double s) const {
     DUNE_THROW(NotImplemented, "regularity not implemented");
   }
+
+  // Whether H(|.|) is smooth at zero
+  bool virtual smoothesNorm() const { return false; }
 };
 
 class RuinaFunction : public NiceFunction {
@@ -164,6 +167,8 @@ class TrivialFunction : public NiceFunction {
   double virtual second_deriv(double) const { return 0; }
 
   double virtual regularity(double) const { return 0; }
+
+  bool virtual smoothesNorm() const { return true; }
 };
 
 // slope in [n-1,n] is n