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Re: Very strange behaviour of ArcTan[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg102675] Re: Very strange behaviour of ArcTan[]
  • From: "Nasser Abbasi" <nma at 12000.org>
  • Date: Tue, 18 Aug 2009 06:09:21 -0400 (EDT)
  • References: <h6bh4m$6ov$1@smc.vnet.net>

"Alexey" <lehin.p at gmail.com> wrote in message 
news:h6bh4m$6ov$1 at smc.vnet.net...
> Hello,
> I just have discovered some strange (buggy?) feature of ArcTan[]
> function in Mathematica 5.2. Try the following;
>
> In[72]:=
> ArcTan[.5,$MachinePrecision]
> ArcTan[.5]
>
> Out[72]=
> 1.53947
>
> Out[73]=
> 0.463648
>
> The expression ArcTan[.5,$MachinePrecision] must (?) give an error but
> in really gives some strange output without any error messages... What
> do you think about this?
>


But it works as per help:

"ArcTan[z] gives the arc tangent tan^-1(z) of the complex number z.
ArcTan[x,y] gives the arc tangent of y/x, taking into account which quadrant 
the point (x,y) is in. "

May be you meant to say:

In[33]:= N[ArcTan[0.5], $MachinePrecision]
Out[33]= 0.4636476090008061

In[34]:= ArcTan[0.5]
Out[34]= 0.4636476090008061


--Nasser 



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