Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2007

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

Search the Archive

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]]]
> ...






  • Prev by Date: Re: export an array of variable depth
  • Next by Date: optimization routine using conjugate gradient (or other) method?
  • Previous by thread: Re: FindInstance puzzler
  • Next by thread: Re: FindInstance puzzler