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MathGroup Archive 1998

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Re: Limit glitch

  • To: mathgroup at smc.vnet.net
  • Subject: [mg14090] Re: Limit glitch
  • From: "Stephen P Luttrell" <luttrell at signal.dra.hmg.gb>
  • Date: Fri, 25 Sep 1998 03:15:18 -0400
  • Organization: Defence Evaluation and Research Agency
  • References: <6u7jdb$snu@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

>I'm wondering whether this has been covered here before. I just noticed
>that Limit often gives wrong results at jump discontinuities. For
>example,  Limit[x/Abs[x], x->0]  returns 1. The pattern seems to be
>that the right-sided limit is always given.
>
>Does anyone know anything about this?


Try this input

Limit[x/Abs[x], x->0,Direction->1]

which explicitly says that the limit is to be approached from below. It
correctly gives the limit as -1.

====================================================

Stephen P Luttrell
Signal Processing and Imagery Department DERA Malvern, St.Andrew's Road
Malvern, United Kingdom, WR14 3PS

+44 (0)1684 894046 (tel)
+44 (0)1684 894384 (fax)
luttrell at signal.dera.gov.uk (email)
http://www.dera.gov.uk/cis5pip/Welcome.html (web)



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