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MathGroup Archive 2006

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Re: ArcTan[-Infinity, y] always returning 0?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69857] Re: ArcTan[-Infinity, y] always returning 0?
  • From: dh <dh at metrohm.ch>
  • Date: Tue, 26 Sep 2006 00:59:12 -0400 (EDT)
  • References: <ef82bq$cuq$1@smc.vnet.net>


Hi,

The Help is o.k., but the Kernel is wrong. Can't see a reason for this, 

looks like an error to me.

I am getting zero too in Mathermatica version 5.1

Daniel



exogen at gmail.com wrote:

> Hi all,

> 

> I'm a little confused about the output I'm getting from ArcTan.

> 

> According to this page about special values for ArcTan:

> http://functions.wolfram.com/ElementaryFunctions/ArcTan2/03/01/01/0005/

> 

> then:

> 

> ArcTan[-Infinity, y] == (2 UnitStep[Re[y]] - 1) Pi

> 

> However, when I use ArcTan where x is -Infinity, it always returns 0:

> 

> In[7]:=

> ArcTan[-Infinity, 1]

> 

> Out[7]=

> 0

> 

> Shouldn't this return Pi?

> 

> The supposed equivalence returns the expected value:

> 

> In[11]:=

> (2 UnitStep[Re[1]]-1) Pi

> 

> Out[11]=

> Pi

> 

> 

> Anyone know what's going on?

> 

> Thanks!

> 



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