#1528 atan2 & asksign

closed
Dan Gildea
None
4
2008-11-30
2008-11-16
Barton Willis
No

When %piargs is true, atan2 sometimes does an asksign.
In atan2(x,x), if x is zero (maybe that's far-fetched, I suppose), you're stuck:

(%i1) atan2(x,x);
Is x positive or negative? pos;
(%o1) %pi/4

As a general rule, I think simplifying functions shouldn't do asksign. Setting %piargs to false, prevents atan2 from doing an asksign (undocumented). But %piargs : false causes bugs in limit and integrate.

Discussion

  • Dan Gildea
    Dan Gildea
    2008-11-30

    as of comm2.lisp rev 1.22, simpatan2 doesn't ask questions:

    (%i2) atan2(x,x);
    (%o2) atan2(x,x)
    (%i3) assume(x>0);
    (%o3) [x > 0]
    (%i4) atan2(x,x);
    (%o4) %pi/4
    (%i5) atan2(-x,-x);
    (%o5) -3*%pi/4

     
  • Dan Gildea
    Dan Gildea
    2008-11-30

    • status: open --> closed
    • assigned_to: nobody --> dgildea