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Re: wrong limit ?

• To: mathgroup at smc.vnet.net
• Subject: [mg76795] Re: [mg76734] wrong limit ?
• From: DrMajorBob <drmajorbob at bigfoot.com>
• Date: Sun, 27 May 2007 05:04:32 -0400 (EDT)
• References: <7513700.1180172543602.JavaMail.root@m35>
• Reply-to: drmajorbob at bigfoot.com

First of all, I suspect you meant

Limit[Coth[x B], B -> +Infinity]

not

Limit[Coth[xB], B -> +Infinity]

There's a very big difference.

Secondly, the limit doesn't exist for ANY non-zero B, since

Limit[Coth[x], x -> -Infinity]
-1

Limit[Coth[x], x -> Infinity]
1

and letting x approach +/- 1/B Infinity makes x B approach +/- Infinity =
 =

(on the real line).

Bobby

On Sat, 26 May 2007 03:43:44 -0500, ventu <nuclearVentu at gmail.com> wrote=
:

> Hi !
> Here's my problem (mathematica 5.0,5.1,5.2):
>
> Limit[Coth[xB], B -> +Infinity]
>
> it doesn't understand.
> mmh. ok I try then:
>
> Limit[Coth[x B], B -> +Infinity, Assumptions ->  Im[x] == 0]
>
> 1
>
> WRONG ! In fact:
>
> Limit[Coth[x B], B -> +Infinity, Assumptions ->  Im[x] == 0 && Re[=
x] <
> 0]
>
> -1
>
> Indeed the correct result should be sign(x). And I couldn't find a way=

> to get it right.
> Do I mistake something?
>
> Thank you in advance,
>
> Davide
>
>
>



-- =

DrMajorBob at bigfoot.com