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Re: Very strange behaviour of ArcTan[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg102681] Re: [mg102656] Very strange behaviour of ArcTan[]
  • From: "Tony Harker" <a.harker at ucl.ac.uk>
  • Date: Tue, 18 Aug 2009 06:10:27 -0400 (EDT)
  • References: <200908171206.IAA06945@smc.vnet.net>

Dear Alexey,

     Why are you surprised by the output? ArcTan is doing exactly what it
should when called with two arguments:

In[1]:= ArcTan[.5, $MachinePrecision]
ArcTan[.5]
$MachinePrecision
$MachinePrecision/.5
ArcTan[%]

Out[1]= 1.53947

Out[2]= 0.463648

Out[3]= 15.9546

Out[4]= 31.9092

Out[5]= 1.53947 

   Tony Harker

]-> -----Original Message-----
]-> From: Alexey [mailto:lehin.p at gmail.com] 
]-> Sent: 17 August 2009 13:07
]-> To: mathgroup at smc.vnet.net
]-> Subject: [mg102656] Very strange behaviour of ArcTan[]
]-> 
]-> 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?
]-> 
]-> 



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