fix assertion

[[Imported from SVN: r6210]]

dune/common/densematrix.hh

@@ -1081,8 +1081,8 @@ namespace Dune
     template <typename MAT, typename V1, typename V2>
     static inline void multAssign(const DenseMatrix<MAT> &matrix, const DenseVector<V1> & x, DenseVector<V2> & ret)
     {
-      assert(x.size() == matrix.rows());
-      assert(ret.size() == matrix.cols());
+      assert(x.size() == matrix.cols());
+      assert(ret.size() == matrix.rows());
       typedef typename DenseMatrix<MAT>::size_type size_type;
 
       for(size_type i=0; i<matrix.rows(); ++i)