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atan/atan2 -- possible changes.
- To: info-lispm at MIT-OZ
- Subject: atan/atan2 -- possible changes.
- From: <Mly at MIT-OZ>
- Date: Wed ,22 Feb 84 17:45:00 EDT
Here's how things stand at the present:
There presently are two functions for taking arctangents,
"atan" and "atan2".
The difference between them is that atan returns a value
in the range 0 to 2*pi, whereas atan2 returns a value in
the range -pi to pi.
(ie atan:(RxR) [0,2]
atan is defined the way it is mainly for maclisp compatibility --
nearly everybody else in the computer languages world (*including
common lisp*) believes that a function called "atan" should return
what the lisp machine's atan2 returns.
So, the $64000 question is:
Would anybody like to vote on whether the definition of atan
should change to be what atan2 is now???
Such a change would not take place immediately, and in the meantime
the compiler could generate a warning saying to use atan2, whose
definition will not change.