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MathGroup Archive 1999

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Re: Real roots and other assumptions...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19992] Re: Real roots and other assumptions...
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Thu, 23 Sep 1999 23:26:33 -0400
  • References: <7s3p1u$ck5@smc.vnet.net> <7s796h$htf@smc.vnet.net> <7sc7u2$c66$1@dragonfly.wolfram.com>
  • Sender: owner-wri-mathgroup at wolfram.com

Kevin J. McCann <kevin.mccann at jhuapl.edu> wrote in message
news:7sc7u2$c66$1 at dragonfly.wolfram.com...
> This does work
>
> Select[{(1 - E)^(1/3)}, Im[#1] == 0 & ]
> {}
>
> as does this:
>
> Select[{(2. + I)*(2. - I)}, Im[#1] == 0 & ]
>
> which gives the odd-looking result
> {5.+0.I}

Kevin:

This is because

(2. + I)*(2. - I)

    5. + 0.*I

and  0. == 0 up to machine precision.

Interestingly enough:

5. + 0.*I   \[Element] Reals

    False

-- snip--

Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565





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