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MathGroup Archive 2005

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Re: Why are the functions different?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55636] Re: Why are the functions different?
  • From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 1 Apr 2005 05:36:08 -0500 (EST)
  • Organization: Uni Leipzig
  • References: <d2g5mg$f2m$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

you mean

f1[x_] = Normal[Series[Tanh[x], {x, 0, 5}]]
f0[x_] := x - x^3/3 + (2*x^5)/15

because if you call f1 with a numeric argument,say 
x->1, you evaluate

Normal[Series[Tanh[1],{1,0,5}]

and this can not work. With you definition the 
Series[] function
is executed in every call of f1[] and this waste 
computation time.

Regards
  Jens

"Helge Stenstroem" 
<helge.stenstrom.NOSPAM at NOSPAMericsson.com> 
schrieb im Newsbeitrag 
news:d2g5mg$f2m$1 at smc.vnet.net...
> How are these two functions (f0 and f1) 
> different? f0 can be plotted,
> but f1 cannot.
>
> f1[x_] := Normal[Series[Tanh[x], {x, 0, 5}]]
> f0[x_] := x - x^3/3 + (2*x^5)/15
>
> When evaluated like this:
> f0[x]
> f1[x]
> they look the same.
>
> The following gives error messages if f0 is 
> replaced by f1.
> Plot[{Tanh[z], f0[z]}, {z, -1, 1}]
>
> (Mathematica 4.1 on Windows 2000)
> -- 
> Helge Stenström
> 



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