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MathGroup Archive 2001

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Re: Limt question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31498] Re: [mg31455] Limt question
  • From: Otto Linsuain <linsuain at andrew.cmu.edu>
  • Date: Thu, 8 Nov 2001 04:54:46 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

I have found that the default setting of the Option Direction in the Limit
function, which is Automatic, is really equivalent to -1. So, it is quite
misleading, perhaps one should always specify what direction one needs, to
be on the safe side. It seem logical that Mathematica could check that the
limit really exists before giving out an answer with the setting
Automatic. Perhaps the reason it doesn't do this is that on the complex
plane there is a continuum of possible directions (Mathematica always
thinks on the complex plane, unless otherwise told, as opposed to us). So
maybe one should use the default setting only where the direction is not
an issue.

Hope it helps, Otto Linsuain.

P.S. One cool thing is that you can specify complex values for Direction,
which then gives you the Limit as you approach the point from a certain
direction on the complex plane. Really neat.

On Wed, 7 Nov 2001, Souvik Banerjee wrote:

> Hello MathGroup,
>
> Why does
>
> Limit[Tan[x], x-> Pi/2] = -infinity ? (Mathematica 4.0, Windows NT)
>
> Thanks,
>
> -Souvik
>
> ps: The Limits with Direction specified is correct though.
>
>
>
>



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