Re: FindInstance puzzler
- To: mathgroup at smc.vnet.net
- Subject: [mg83654] Re: FindInstance puzzler
- From: Tom Burton <news at brahea.com>
- Date: Tue, 27 Nov 2007 06:15:54 -0500 (EST)
A diagnosis seems easy enough, but so far a cure eludes me. Observe
that your conditions contain the radical Sqrt[z1^2+4z2]. Your
invocation of FindInstance asks it to assume that, not only the
variables but also all function values are real, in particular Sqrt,
implying that z1^2+4z2>0. Indeed, all points found satisfy this
condition. No puzzler here. Unfortunately, when I try the suggested
variation to relax this assumption,
RegionPlot[conds,{z1,-.75,2.25},{z2,-1.25,1.25},PlotPoints->90,
Epilog->Point[{z1,z2}/.
FindInstance[conds&&Element[{z1,z2},Reals],{z1,z2},10^3]
]]
the kernel goes out to lunch. I hope someone has a better idea.
Tom
When responding, please replace news with my first initial and full
last name, as one word.
Tom Burton
> ...
> RegionPlot[conds, {z1, -.75, 2.25}, {z2, -1.25, 1.25}, PlotPoints -
> > 90,
> Epilog -> Point[{z1, z2} /. FindInstance[conds, {z1, z2}, Reals,
> 10^3]]]
> ...