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Re: Very strange behaviour of ArcTan[]

• To: mathgroup at smc.vnet.net
• Subject: [mg102667] Re: [mg102656] Very strange behaviour of ArcTan[]
• From: Adriano Pascoletti <adriano.pascoletti at dimi.uniud.it>
• Date: Tue, 18 Aug 2009 06:07:53 -0400 (EDT)
• References: <200908171206.IAA06945@smc.vnet.net>

Alexey,

ArcTan[x,y] gives the arc tangent y/x taking into account which quadrant the
point (x,y) is in

In[1]:= $MachinePrecision
Out[1]= 15.9546


In[4]:= ArcTan[0.5, $MachinePrecision]
Out[4]= 1.5394676360951292


In[5]:= ArcTan[$MachinePrecision/0.5]
Out[5]= 1.539467636095129


Adriano Pascoletti


2009/8/17 Alexey <lehin.p at gmail.com>

> 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?
>
>

• References:
  • Very strange behaviour of ArcTan[]
    • From: Alexey <lehin.p@gmail.com>