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

MathGroup Archive 2013

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

Search the Archive

Re: Wrong Answer

  • To: mathgroup at smc.vnet.net
  • Subject: [mg130637] Re: Wrong Answer
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sun, 28 Apr 2013 00:59:19 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • Delivered-to: l-mathgroup@wolfram.com
  • Delivered-to: mathgroup-outx@smc.vnet.net
  • Delivered-to: mathgroup-newsendx@smc.vnet.net
  • References: <20130427030938.151746A1A@smc.vnet.net>

If I use exact rationals for the parameters --

  r := {px -> 1/2, py -> 1/2, vx -> 1/2, vy -> 1/2}

-- then Solve[p,t]/.r gives division by 0 errors.

That's with Mathematica 9.0.1 under OS X (10.8.3).

On Apr 26, 2013, at 11:09 PM, christopher arthur <chris.arthur1 at gmail.com> wrote:

> Hello,
>
> I've discovered that Solve[] gives me the wrong answer for some
> polynomial equations.  For example, consider the following equation,
> which should have exactly one positive, real answer for t. 
>
> p:=(px + t vx)^4 + (py + t vy)^4==1
> r:={px->0.5,py->0.5,vx->0.5,vy->0.5}
> NSolve[p/.r,t]
>
> NSolve gives the right answers if I substitute for px,py,vx and vy
> before solving.  On the other hand, if I use Solve[] this way:
>
> Solve[p,t]/.r
>
> I get a different answer, and it's not correct.
> Does Solve[] just malfunction with quartic polynomials or is there
> something else happening?
>
> Chris
>
> mathematica 5.2
>
> Solve[p]

---
Murray Eisenberg                                    murray at math.umass.edu
Mathematics & Statistics Dept.      
Lederle Graduate Research Tower            phone 413 549-1020 (H)
University of Massachusetts                               413 545-2838 (W)
710 North Pleasant Street                         fax   413 545-1801
Amherst, MA 01003-9305








  • References:
    • Wrong Answer
      • From: christopher arthur <chris.arthur1@gmail.com>
  • Prev by Date: Re: Convolve: Different Looking Results. (2)
  • Next by Date: Re: Mathematica-assisted learning was .. Re: Speak errors
  • Previous by thread: Wrong Answer
  • Next by thread: Re: Wrong Answer