John Machin <[EMAIL PROTECTED]> writes: > 1. What is an "interchange"?
Swapping two elements during the sort. > 2. Without a definition that refers only to to the input and output, > one would have to say that "interchange" implies "event" and so the > number of interchanges would depend on the sorting method. The number of interchanges depends on the sorting method, but whether the number is odd or even is invariant. Every permutation of elements is either an odd permutation or an even permutation. > 3. Of what practical use (or even esoteric academic interest) is the > parity of the number of interchanges? It is of considerable interest in combinatorics. The group of even permutations on N elements is called the alternating group A(N). It's an order-2 subgroup of the symmetric group S(N) which is the group of all the permutations on N elements. The odd permutations are of course a coset of A(N). -- http://mail.python.org/mailman/listinfo/python-list
