Re: Why is this so?
- To: mathgroup at smc.vnet.net
- Subject: [mg15328] Re: [mg15304] Why is this so?
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Fri, 8 Jan 1999 04:15:18 -0500
- Organization: Universitaet Leipzig, Institut fuer Informatik
- References: <199901040721.CAA14333@smc.vnet.net.>
- Sender: owner-wri-mathgroup at wolfram.com
Hi Chester,
no it is not true that (-125)^(1/3) == -5
it is true that (-5)^3 == -125 but there are two other numbers (5
*(-1)^1/3) and (-5*(-1)^(2/3).
Mathematica need to know witch one you mean.
There is a RealOnly package Miscellaneous`RealOnly` that may help you.
Regards
Jens
Chester Lin wrote:
> The following in/out does not make sense to me:
>
> Clear[f, x]
> f[x_] := x^(1/3)
> Plot[f[x], {x, -125, 125}]
>
> Plot::plnr : f[x] is not a machine-size real number at x = -125..
> Plot::plnr : f[x] is not a machine-size real number at x = -114.858.
> Plot::plnr : f[x] is not a machine-size real number at x = -103.798.
> General::stop :
> Further output of Plot::plnr will be suppressed during this
> calculation.
>
> Isn't it true that (-125)^(1/3) == -5?
>
> Why do I get this strange result?
>
> I am using Mathematica 3.01 for Students on Macintosh.
>
> Thanks for any info.
>
> Chester Lin
> chester at nicco.sscnet.ucla.edu