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- Newsgroups: comp.theory
- Path: sparky!uunet!wupost!darwin.sura.net!ra!AIC.NRL.Navy.Mil!hoey
- From: hoey@AIC.NRL.Navy.Mil (Dan Hoey)
- Subject: Re: Real Numbers vs. Rational Numbers?
- Message-ID: <9212281124.hoey@aic.nrl.navy.mil>
- Sender: usenet@ra.nrl.navy.mil
- Organization: Naval Research Laboratory, Washington, DC
- References: <1992Dec16.095412.19570@tom.rz.uni-passau.de> <1992Dec17.114502@di.epfl.ch> <1277@zogwarg.etl.army.mil> <1992Dec24.094657.20379@ringer.cs.utsa.edu>
- Date: Mon, 28 Dec 1992 16:24:49 GMT
- Lines: 44
-
- I wrote:
-
- >One interesting complexity non-result is the open question:
-
- > Is the travelling salesman problem with cities on an integer
- > lattice in NP?
-
- >The numbers are non only real, but algebraic. Not only algebraic, but
- >constructible!
-
- And djimenez@ringer.cs.utsa.edu (Daniel Jimenez) replied:
-
- > Hmm. I think you mean P, not NP (obviously it's in NP).
-
- No, I meant NP. And it is sufficiently nonobvious to be a decades-old
- open problem.
-
- The hard part about showing this is in NP is the problem of finding
- which of two candidate tours is shorter. In particular, the problem
-
- Given two sets {a1, ..., an} and {b1, ..., bn} of positive
- integers, determine whether
-
- sqrt(a1)+sqrt(a2)+...+sqrt(an) > sqrt(b1)+sqrt(b2)+...+sqrt(bn)
-
- is not known to be in NP or co-NP. If you have any good way of
- showing how a NDTM can determine that question in polynomial time, you
- should publish it. You may, if you wish, provide a method that only
- works when each of the ai and bi is the sum of two squares. (If that
- helps, the result will be even more amazing.)
-
- > Anyway, it seems like this problem is NP-complete....
-
- It is well known as an NP-hard problem. In fact, given n points in
- the integer lattice, the question of whether there exists a
- Hamiltonian circuit of length n--i.e., consisting of unit-length
- edges--is known to be NP-complete. This is how it is shown that
- Euclidean TSP is NP-complete.
-
- I don't have it with me, but I believe you will find all of this in
- _The_Traveling_Salesman_Problem_, Lawler et. al. (Eds.), Wiley, '85.
-
- Dan Hoey
- Hoey@AIC.NRL.Navy.Mil
-