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MathGroup Archive 2006

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Re: Re: Limit bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg65961] Re: [mg65911] Re: [mg65904] Limit bug?
  • From: "Erickson Paul-CPTP18" <Paul.Erickson at Motorola.com>
  • Date: Mon, 24 Apr 2006 06:02:37 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com
  • Thread-index: AcZm0GF3Ej5K8sXkQ/KBlpJC2J0NwAAc7WXg

An explanation? No, but ...

There appear to be a several other ways to force the evaluation, like:
Limit[x - Log[Cosh[x]], x -> â??] // FullSimplify
or noting the negative can be pulled outside, so 
-Limit[ Log[Cosh[x]] - x, x -> Infinity]

But I do find it curious since:
In[5]:=
Limit[ Log[Cosh[x]] - x, x -> Infinity]//Trace

Out[5]=
{{Log[Cosh[x]]-x,-x+Log[Cosh[x]]},{{â??,â??},x\[Rule]â??,x\[Rule]â??},Limit[-x+Log[
      Cosh[x]],x\[Rule]â??],-Log[2]}

Simplifies to the same form (but each term negative) ...

Paul

-----Original Message-----
From: Bob Hanlon [mailto:hanlonr at cox.net] 
To: mathgroup at smc.vnet.net
Subject: [mg65961] [mg65911] Re: [mg65904] Limit bug?

I don't know why the second form does not evaluate but you can force it with TrigToExp

Limit[TrigToExp[x - Log[Cosh[x]]], x->Infinity]

log(2)


Bob Hanlon

> 
> From: "Ray Koopman" <koopman at sfu.ca>
To: mathgroup at smc.vnet.net
> Subject: [mg65961] [mg65911] [mg65904] Limit bug?
> 
> Does anyone have an explanation for this?
> I was expecting Out[2] to be Log[2].
> 
> In[1]:= Limit[ Log[Cosh[x]] - x, x -> Infinity]
> 
> Out[1]= -Log[2]
> 
> In[2]:= Limit[ x - Log[Cosh[x]], x -> Infinity]
> 
> Out[2]= Limit[x-Log[Cosh[x]],x\[Rule]\[Infinity]]
> 
> 


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