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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.postscript
Subject: Re: -100 0 atan ==> 270 or -90?
Organization: Decebal Computing
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Date: Sat, 03 Aug 2013 10:04:54 +0200
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Op zaterdag 3 aug 2013 06:23 CEST schreef luser:

> I've started writing up a test program for all operators, 
> mostly using the example snippets from the manual.
>
> And I've run into a difference between the Red Book (PLRM 1ed) 
> and the GNU C library in the value returned by atan.
>
> The Red Book says:
>
> -100 0 atan => 270.0
>
> But atan2(3) (after suitable conversions) gives me -90.0
>
> Is this serious? And, if so, what (if anything) should I do about
> it?

It looks like postscript does a modulo 360. Which in certain
definitions gives a value between 0 and modVal. The funny thing being
that mod gives a value between -modVal and modVal.

So I would say it is a bug.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof