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MathGroup Archive 1995

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Re: How to solve system of inequalities?

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg1102] Re: How to solve system of inequalities?
  • From: gwyn at arl.mil (Doug Gwyn )
  • Date: Sun, 14 May 1995 23:01:36 -0400
  • Organization: U.S. Army Research Laboratory APG, MD.

In article <3oker8$jh7 at news0.cybernetics.net>, jeff at econ.berkeley.edu wrote:
->Hi.  I have a system of linear inequlities specified symbolically.
->I want to test whether they are consistent.
->But if I enter
->	In[2] y<x && x<y
->I get back the unhelpful
->	Out[2] y < x && x < y
->Apparently Mathematica cannot deduce that this is impossible.

I'm pretty sure the *general* question is not effectively computable.
If the specific need is for a chain of simple variables as above and
not more complicated expressions, then this becomes a well-ordering
issue and what *I* would do to solve it would be to use UNIX "tsort",
or if it had to be in Mathematica I'd implement a topological sorting
algorithm.


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