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MathGroup Archive 2006

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Re: Problem with Limit

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66859] Re: [mg66805] Problem with Limit
  • From: gardyloo <gardyloo at mail.wsu.edu>
  • Date: Thu, 1 Jun 2006 06:56:01 -0400 (EDT)
  • References: <200605311030.GAA13862@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

I've plotted the function "t" as defined below (at least I think I've 
correctly changed all of the squares correctly) as a function of "g", 
for some arbitrarily chosen values of the parameters m1, k, and m2, and 
it appears that the limit of zero as g->0 is incorrect.

      C.O.


Tony Harker wrote:
> Can anybody explain why, for 
>
> t =Sqrt[(k*m1 + k*m2 + m1*g + m2*g - 
>          (1/2)*Sqrt[4*(m1 + m2)^2*(k + g)^2 - 16*k*m1*m2*(k + 2*g)])/
>         (m1*m2)]/(1 + (k*m1 - k*m2 + m1*g - m2*g + 
>           (1/2)*Sqrt[4*(m1 + m2)^2*(k + g)^2 - 16*k*m1*m2*(k + 2*g)])^2/
>         (4*m1*m2*g^2)) + Sqrt[(k*m1 + k*m2 + m1*g + m2*g + 
>          (1/2)*Sqrt[4*(m1 + m2)^2*(k + g)^2 - 16*k*m1*m2*(k + 2*g)])/
>         (m1*m2)]/(1 + ((-k)*m1 + k*m2 - m1*g + m2*g + 
>           (1/2)*Sqrt[4*(m1 + m2)^2*(k + g)^2 - 16*k*m1*m2*(k + 2*g)])^2/
>         (4*m1*m2*g^2));
>
> Limit[t, g -> 0]
> Limit[Together[t], g -> 0]
>
> both give zero, whereas
>
> Limit[Simplify[Together[t]], g -> 0]
>
> gives a non-zero result? This is with Mathe4matica 5.2.
>
>
> Dr A.H. Harker
> Department of Physics and Astronomy
> University College London
> Gower Street
> London
> WC1E 6BT
>
>
>
>   


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Curtis Osterhoudt
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