Minimizing the sum(permutation*inverse)
Leroy Quet
qq-quet at mindspring.com
Mon May 15 17:34:29 CEST 2006
Regarding the sci.math thread:
http://groups.google.com/group/sci.math/browse_thread/thread/6cf265b0d0e2f1
57
Let {b(k)} be a permutation of {1,2,3,...,n}.
Let {c(k)} be the inverse-permutation of {b(k)}.
(ie. b(c(j)) =j, for every j.)
What is the minimum possible sum:
sum{k=1 to n} b(k) * c(k) ?
For example, if b is:
[1,2,3],
[2,1,3],
[3,2,1],
each give a sum of 14 (since each of these permutations is its own
inverse).
But
[2,3,1],
[3,1,2],
(which are inverses of each other)
both give a sum of 11.
I get (possibly erroneously) that the sequences of minimum sums begins:
1, 5, 11, 20, 35,...
Could someone please calculate/submit this sequence (unless it is already
in the EIS, of course).
thanks,
Leroy Quet
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