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MathGroup Archive 1998

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Re: BUG in Calculus`VectorAnalysis` CoordinatesFromCartesian?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg15042] Re: [mg15010] BUG in Calculus`VectorAnalysis` CoordinatesFromCartesian?
  • From: David Withoff <withoff>
  • Date: Wed, 9 Dec 1998 04:12:25 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

> I worked a little bit with the Calculus`VectorAnalysis package, and
> think I found a minor BUG.
> 
> Needs["Calculus`VectorAnalysis`"];
> SetCoordinates[Spherical];
> 
> ein={e,45Degree,0Degree};
> CoordinatesToCartesian[ein]
> Out={e/Sqrt[2], 0, e/Sqrt[2]}
> 
> CoordinatesFromCartesian[%]
> Out={Sqrt[e^2], ArcCos[e/(Sqrt[2]*Sqrt[e^2])], ArcTan[e/Sqrt[2], 0]}
> 
> The 3rd list entry (Pphi) contains the ArcTan with an invalid argument.
> 
> Marcus Heidkamp
> 
> msheidka at physics.utexas.edu

The result with ArcTan[e/Sqrt[2], 0] is correct.  Zero is a valid
argument here.  If e is real, ArcTan[e/Sqrt[2], 0] is zero for e>0 and
Pi for e < 0.  Perhaps you were thinking of something else.

Dave Withoff
Wolfram Research


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