ArcTan(x,y)?

[Han]

(04-06-2017 03:30 PM)StephenG1CMZ Wrote:  

(04-05-2017 10:41 PM)KeithB Wrote:  So if the limit of atan2(x,x) as x approaches 0 is 45, maybe that is what atan2() should return?

Clearly, discontinuities near 0 cannot be avoided - I have even seen it suggested online that one could scale values and use integer arithmetic to work around. I am beginning to wonder whether returning an error might be useful. But many Atan2 implementations do return 0, so changing to return 45 instead would introduce compatibility issues.

Care should be taken when evaluating limits of 2-variable functions. See second-to-last post in:

http://www.hpmuseum.org/forum/thread-7346.html

atan(x/x) is 45, but atan(0/x) is 0 and atan(y/0) is 90*sign(y) (EDIT: I erroneously wrote "infinite" earlier). The limit does not exist so mathematically atan(0/0) is undefined.