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Re: Very strange behaviour of ArcTan[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg102660] Re: Very strange behaviour of ArcTan[]
  • From: "David W. Cantrell" <DWCantrell at sigmaxi.net>
  • Date: Tue, 18 Aug 2009 06:06:34 -0400 (EDT)
  • References: <h6bh4m$6ov$1@smc.vnet.net>

Alexey <lehin.p at gmail.com> 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

No. Look at the documentation for ArcTan. There is a very useful version of
ArcTan which takes _two_ arguments. And of course $MachinePrecision merely
supplies a numerical value for the second argument.

> but
> in really gives some strange output without any error messages... What
> do you think about this?

There's nothing wrong.

David


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