Dear GAP Forum members,

On Feb. 22. Aaron Mackey asked:

I would be grateful for any references or pointers regarding the
enumeration algorithm used by NrArrangements.

I apologize that it has taken until now to contact Martin Schoenert
who had written that function, but anyhow here is his reply:

The algorithm is indeed rather straightforward. Basically the same
algorithm is used to compute the number of combinations, except that
NrCombinations does not take ordering into account. Of course this
algorithm is only used for arrangments of multi-sets. The number of
arrangments of a proper set uses a well known closed formula.

A description of the algorithm can be found in

>Concrete Mathematics: A Foundation For Computer Science
> Ronald L. Graham, Donald E. Knuth, Oren Patashnik

Martin Schoenert

Joachim Neubueser