• 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)
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```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:
• From: christopher arthur <chris.arthur1@gmail.com>
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