Add using std::sqrt or std::abs directives
This MR adds using directives for the use of std::sqrt or std::abs. This is needed because other names in the namespace Dune are probably found before the names in the namespace std.
This MR adds using directives for the use of std::sqrt or std::abs. This is needed because other names in the namespace Dune are probably found before the names in the namespace std.
merged