The sole purpose of this namespace is to be able to import all functions and symbols that are expected to be used within operator() for indexing and slicing. If you already imported the whole Eigen namespace:
then you are already all set. Otherwise, if you don't want/cannot import the whole Eigen namespace, the following line:
is equivalent to:
static const Eigen::internal::all_t all
auto lastN(SizeType size, IncrType incr) -> decltype(seqN(Eigen::placeholders::last-(size-fix< 1 >()) *incr, size, incr))
auto seq(FirstType f, LastType l, IncrType incr)
ArithmeticSequence< typename internal::cleanup_index_type< FirstType >::type, typename internal::cleanup_index_type< SizeType >::type, typename internal::cleanup_seq_incr< IncrType >::type > seqN(FirstType first, SizeType size, IncrType incr)