Merge branch 'feature/abs_gridfunction' into 'master'

add expression abs() to gridfunctions

See merge request !7

src/amdis/gridfunctions/OperationsGridFunction.hpp

@@ -113,6 +113,13 @@ namespace AMDiS
     return invokeAtQP(Operation::Clamp<T>{lo,hi}, FWD(v));
   }
 
+  template <class T,
+    REQUIRES(Concepts::AnyGridFunction<T>)>
+  auto abs(T&& value)
+  {
+    return invokeAtQP([](auto const& v) { using std::abs; return abs(v); }, FWD(value));
+  }
+
   /// \brief Applies \ref Operation::Sqr to GridFunction. \relates FunctorGridFunction
   template <class T,
     REQUIRES(Concepts::AnyGridFunction<T>)>