Make the test suite work again

src/test-gradient-method-nicefunction.hh

+#include <dune/tectonic/nicefunction.hh>
+
+namespace Dune {
+class MyFunction : public NiceFunction {
+  double virtual second_deriv(double) const {
+    assert(false);
+    return 0;
+  }
+
+  double virtual regularity(double) const {
+    assert(false);
+    return 0;
+  }
+};
+
+class LinearFunction : public MyFunction {
+public:
+  LinearFunction(double a) : coefficient(a) {}
+
+  void virtual evaluate(double const &x, double &y) const {
+    y = coefficient * x;
+  }
+
+  double virtual leftDifferential(double s) const { return coefficient; }
+
+  double virtual rightDifferential(double s) const { return coefficient; }
+
+  double virtual second_deriv(double) const { return 0; }
+
+  double virtual regularity(double s) const { return 0; }
+
+private:
+  double const coefficient;
+};
+
+template <int slope> class SampleFunction : public MyFunction {
+public:
+  void virtual evaluate(double const &x, double &y) const {
+    y = (x < 1) ? x : (slope * (x - 1) + 1);
+  }
+
+  double virtual leftDifferential(double s) const {
+    return (s <= 1) ? 1 : slope;
+  }
+
+  double virtual rightDifferential(double s) const {
+    return (s < 1) ? 1 : slope;
+  }
+};
+
+class SteepFunction : public MyFunction {
+public:
+  void virtual evaluate(double const &x, double &y) const { y = 100 * x; }
+
+  double virtual leftDifferential(double s) const { return 100; }
+
+  double virtual rightDifferential(double s) const { return 100; }
+};
+
+// slope in [n-1,n] is n
+class HorribleFunction : public MyFunction {
+public:
+  void virtual evaluate(double const &x, double &y) const {
+    double const fl = floor(x);
+    double const sum = fl * (fl + 1) / 2;
+    y = sum + (fl + 1) * (x - fl);
+  }
+
+  double virtual leftDifferential(double x) const {
+    double const fl = floor(x);
+    if (x - fl < 1e-14)
+      return fl;
+    else
+      return fl + 1;
+  }
+
+  double virtual rightDifferential(double x) const {
+    double const c = ceil(x);
+    if (c - x < 1e-14)
+      return c + 1;
+    else
+      return c;
+  }
+};
+
+// slope in [n-1,n] is log(n+1)
+class HorribleFunctionLogarithmic : public MyFunction {
+public:
+  void virtual evaluate(double const &x, double &y) const {
+    y = 0;
+    size_t const fl = floor(x);
+    for (size_t i = 1; i <= fl;)
+      y += std::log(
+          ++i); // factorials grow to fast so we compute this incrementally
+
+    y += std::log(fl + 2) * (x - fl);
+  }
+
+  double virtual leftDifferential(double x) const {
+    double const fl = floor(x);
+    if (x - fl < 1e-14)
+      return std::log(fl + 1);
+    else
+      return std::log(fl + 2);
+  }
+
+  double virtual rightDifferential(double x) const {
+    double const c = ceil(x);
+    if (c - x < 1e-14)
+      return std::log(c + 2);
+    else
+      return std::log(c + 1);
+  }
+};
+}

src/test-gradient-method.cc

@@ -11,6 +11,7 @@
 #include <dune/tnnmg/problem-classes/bisection.hh>
 
 #include <dune/tectonic/samplefunctional.hh>
+#include "test-gradient-method-nicefunction.hh"
 
 template <int dim>
 double functionTester(Dune::SampleFunctional<dim> J,