[geometry] Add function to compute a geometry's diameter

dumux/common/geometry/CMakeLists.txt

 install(FILES
 boundingboxtree.hh
 boundingboxtreeintersection.hh
+diameter.hh
 geometricentityset.hh
 geometryintersection.hh
 grahamconvexhull.hh

dumux/common/geometry/diameter.hh

+/*****************************************************************************
+ *   See the file COPYING for full copying permissions.                      *
+ *                                                                           *
+ *   This program is free software: you can redistribute it and/or modify    *
+ *   it under the terms of the GNU General Public License as published by    *
+ *   the Free Software Foundation, either version 3 of the License, or       *
+ *   (at your option) any later version.                                     *
+ *                                                                           *
+ *   This program is distributed in the hope that it will be useful,         *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of          *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           *
+ *   GNU General Public License for more details.                            *
+ *                                                                           *
+ *   You should have received a copy of the GNU General Public License       *
+ *   along with this program.  If not, see <http://www.gnu.org/licenses/>.   *
+ *****************************************************************************/
+/*!
+ * \file
+ * \ingroup Common
+ * \brief A function to compute a geometry's diameter, i.e.
+ *        the longest distance between points of a geometry
+ */
+#ifndef DUMUX_GEOMETRY_DIAMETER_HH
+#define DUMUX_GEOMETRY_DIAMETER_HH
+
+#include <algorithm>
+
+namespace Dumux {
+
+/*!
+ * \ingroup Common
+ * \brief Computes the longest distance between points of a geometry
+ * \note Useful e.g. to compute the maximum cell diameter of a grid
+ */
+template<class Geometry>
+typename Geometry::ctype diameter(const Geometry& geo)
+{
+    using std::max;
+    typename Geometry::ctype h = 0.0;
+    for (std::size_t i = 0; i < geo.corners(); ++i)
+        for (std::size_t j = i + 1; j < geo.corners(); ++j)
+            h = max(h, (geo.corner(i)-geo.corner(j)).two_norm());
+
+    return h;
+}
+
+} // end namespace Dumux
+
+#endif