maximum_n_ind lives in PDL::Ufunc (somewhat to my surprise). To find this sort of information, in perldl do:

pdl> ?? maximum_n_ind
maximum_n_ind   P::Ufunc  Returns the index of `m_size' maximum elemen
+ts. As of
                          2.077, you can specify how many by either pa
+ssing in
                          an ndarray of the given size (DEPRECATED - w
+ill be
                          converted to indx if needed and the input ar
+g will be
                          set to that), or just the size, or a null an
+d the
                          size.
maxover_n_ind   P::Ufunc  Synonym for maximum_n_ind.
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