Boost LA

#include <boost/la/vector_mul_scalar.hpp>

#include <boost/la/deduce_vector.hpp>

namespace
boost
    {
    namespace
    la
        {
        //Only enabled if: is_vector<A>::value
        template <class A>
        typename deduce_vector<A>::type
        operator*( A const & a, vector_traits<A>::scalar_type s );
        }
    }