[Date Index] [Thread Index] [Author Index]

FindInstance puzzler

• To: mathgroup at smc.vnet.net
• Subject: [mg83633] FindInstance puzzler
• From: Mark Fisher <particlefilter at gmail.com>
• Date: Mon, 26 Nov 2007 03:49:26 -0500 (EST)

Hi all,

I'm puzzled by the results of FindInstance which seems to restrict its
results to a subregion of the valid space.

conds = And @@
  Append[Thread[(Abs[L] /. Solve[1 - z1 L - z2 L^2 == 0, L]) >= 1],
   z1 + z2 >= 0];

RegionPlot[conds, {z1, -.75, 2.25}, {z2, -1.25, 1.25}, PlotPoints ->
90,
 Epilog ->  Point[{z1, z2} /. FindInstance[conds, {z1, z2}, Reals,
10^3]]]

I suppose this isn't a bug, because the results of FindInstance are
all valid, but nevertheless I find it unpleasing (to say the least)
that part of the valid space seems to get no representation. It means
that FindInstance is of limited use for exploring such spaces.

--Mark

• Follow-Ups:
  • Re: FindInstance puzzler
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>