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Re: Mathematica and Lisp

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  • Subject: [mg120041] Re: Mathematica and Lisp
  • From: Richard Fateman <fateman at>
  • Date: Wed, 6 Mar 2013 05:55:12 -0500 (EST)
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On 3/5/2013 7:54 PM, djmpark wrote:
> Reverse the order of what? ArcTan of one argument has only one argument and
> how can that be reversed? What has two arguments is the coordinate
> specification {x, y} and they are not reversed in ArcTan[x, y].
> It is the one argument form ArcTan[y/x] that seems poorly designed and would
> probably only be used when one knows the quotient and not x and y - so there
> wouldn't be anything to reverse.
> David Park
> djmpark at
> From: Richard Fateman [mailto:fateman at]
>   (simple example:  why does Mathematica reverse the order of arguments to
> arctan of 2 args?)
> RJf
ArcTan[x,y]  in Mathematica gives the ArcTan[y/x] but in the correct 
atan2 (y,x) in FORTRAN gives the arctangent of y/x). Note the order of 
             in C++
             in Pascal
             in Java
             in Lisp  (atan y x)
             in PHP
             in Python v 3.3.0
             in Ruby

I was able to find just one programming language that agrees with the 
order in Mathematica.
That is Microsoft's Excel. Now it could be that compatibility with Excel is
more important than compatibility with those other languages. Google 
docs has to
use the same order as Excel, but I think it is generally recognized as being
compatible with an error.
Just sayin'.

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