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