Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2001
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2001

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

Search the Archive

Re: Solutions that are not solutions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32087] Re: Solutions that are not solutions
  • From: "M.Weber" <matweber at indiana.edu>
  • Date: Sat, 22 Dec 2001 04:23:07 -0500 (EST)
  • Organization: Indiana University, Bloomington
  • References: <9vuth9$of2$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

PSi wrote:

> I'm trying to solve a system as follows:
> X={{0,y,z},{y,x,t},{u,v,w}}
> A={{1,1,a},{0,1,0},{0,0,1}}
> Solve[{X.A==Transpose[A].X, Det[X]==1},
> {x,y,z,t,u,v,w}]
>
> Mathematica 4.1 gives two solutions:
> X1={{0,y,0},{y,x,t},{0,v,-1/y^2}}
> and
> X2={{0,y,a*y},{y,(a*t*y^2-1+a*v*y^2-w*y^2)/(a*y)^2,t},
> {a*y,v,w}}
>
> However, X1 is not a solution:
> X1.A-Transpose[A].X1={{0,0,0},{0,0,a*y},{0,-a*y,0}}
>
> Could anybody explain this behaviour?
> Thanks
> PSi

You might want to include 'a' as a variable. However, this is clearly a
bug. I have found similar problems in Version 3 and 4.1 where Mathematica
returns more 'solutions' than exist or where reduce returns an inequivalent
system. Very annoying. But we all think of
course that better graphics has the priority, right?

Matthias



  • Prev by Date: RE: Replacement Rule
  • Next by Date: Re: solutions that are not solutions
  • Previous by thread: Re: Solutions that are not solutions
  • Next by thread: Re: solutions that are not solutions