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MathGroup Archive 2006

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Re: Erf[InverseErf] -- making a function and its inverse cancel

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69015] Re: Erf[InverseErf] -- making a function and its inverse cancel
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Sat, 26 Aug 2006 04:40:05 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <ecoq4t$35n$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

mktippett at gmail.com wrote:
> How can I get an expression like Erf[InverseErf[0,1/3]] to simplify to
> 1/3?
> 
> Cos[ArcCos[1/3]] gives 1/3. Is there some assumption that I'm missing?
> 
> thanks,
> Mike
> 

For reason of efficiency, Mathematica does not call systematically the 
simplification rules. You must nudge Mathematica to force the 
simplification.

In[1]:=
FullSimplify[Erf[InverseErf[0, 1/3]]]

Out[1]=
1
-
3

In[2]:=
N[Erf[InverseErf[0, 1/3]]]

Out[2]=
0.333333

HTH,
Jean-Marc


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