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Re: wrong limit ? (2)

• To: mathgroup at smc.vnet.net
• Subject: [mg76803] Re: wrong limit ? (2)
• From: dimitris <dimmechan at yahoo.com>
• Date: Sun, 27 May 2007 05:08:40 -0400 (EDT)
• References: <f38tdj$ish$1@smc.vnet.net>

You could add the rule to Limit.

In[1]:=
Unprotect[Limit];
Limit[Coth[(a_.)*(o_)], o_ -> Infinity, Assumptions ->
Element[a,Reals]] := Sign[a]

Dimitris




 /  ventu       :
> 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