added negation operator for FieldMatrix

src/amdis/common/FieldMatVec.hpp

@@ -197,6 +197,9 @@ namespace Dune
   template <class T, int M, int N>
   FieldMatrix<T,N,M> trans(FieldMatrix<T, M, N> const& A);
 
+  template <class T, int M, int N>
+  FieldMatrix<T,M,N> operator-(FieldMatrix<T, M, N> A);
+
 
   template <class T, int M, int N, class S,
     std::enable_if_t<std::is_convertible<S,T>::value, int> = 0>

src/amdis/common/FieldMatVec.inc.hpp

@@ -349,6 +349,11 @@ FieldMatrix<T,N,M> trans(FieldMatrix<T, M, N> const& A)
   return At;
 }
 
+template <class T, int M, int N>
+FieldMatrix<T,M,N> operator-(FieldMatrix<T,M,N> A)
+{
+  return A *= -1;
+}
 
 template <class T, int M, int N, class S,
   std::enable_if_t<std::is_convertible<S,T>::value, int>>