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Re: Very strange behaviour of ArcTan[]

• To: mathgroup at smc.vnet.net
• Subject: [mg102682] Re: Very strange behaviour of ArcTan[]
• From: Szabolcs Horvát <szhorvat at gmail.com>
• Date: Tue, 18 Aug 2009 06:10:39 -0400 (EDT)
• References: <h6bh4m$6ov$1@smc.vnet.net>

On 2009.08.17. 14:06, Alexey wrote:
> 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?

What are you trying to do?  According to the docs, "ArcTan[x,y] gives 
the arc tangent of y/x, taking into account which quadrant the point 
(x,y) is in."