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MathGroup Archive 2001

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Re: ArcTan[x, 0] With Numeric Values

  • To: mathgroup at smc.vnet.net
  • Subject: [mg30561] Re: [mg30544] ArcTan[x, 0] With Numeric Values
  • From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
  • Date: Wed, 29 Aug 2001 01:40:05 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

You seem to have discovered a (minor) bug, which causes Simplify to 
misbehave for certain specific numeric inputs: namely Pi or E (and maybe 
others) but not 2Pi, E/2 etc. For example:

In[2]:=
Simplify[{ArcTan[2Pi,0],ArcTan[Pi/2,0],ArcTan[E/2,0],ArcTan[E,0],
     ArcTan[Pi,0]}]

Out[2]=
{0, 0, 0, ArcTan[E, 0], ArcTan[Pi, 0]}

Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/

On Tuesday, August 28, 2001, at 05:54  PM, David Park wrote:

> Dear MathGroup,
>
> Why does this two argument form of ArcTan not automatically simplify 
> with
> numeric input? It does simplify with number input.
>
> {ArcTan[5, 0], ArcTan[Sqrt[5], 0], ArcTan[Pi, 0]}
> Simplify[%]
> FullSimplify[%]
>
> {0, ArcTan[Sqrt[5], 0], ArcTan[Pi, 0]}
> {0, 0, ArcTan[Pi, 0]}
> {0, 0, 0}
>
> One would normally expect the same simplification to automatically 
> occur in
> all three of these cases.
>
> David Park
> djmp at earthlink.net
> http://home.earthlink.net/~djmp/
>
>
>



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