** [bugs:#2620] atan2(y,x)+atan2(-y,x) doesn't always return 0**

**Status:** open

**Created:** Mon Aug 05, 2013 03:11 PM UTC by David Ronis

**Last Updated:** Mon Aug 05, 2013 03:11 PM UTC

**Owner:** nobody

I'm running the git master (currently at 5.28.0_137_ge1a2891 using CLISP 2.49). I have a project that generates various atan2's. In trying to simplify an expression I noticed that something like:

atan2(y,x)-atan2(-y,x);

doesn't always return zero (which is should no matter what the signs or x or y are).

Here's a test case:

ans1:atan2(y,x)+atan2(-y,x);

(%o1) 0

(%i2) assume(y>0);

(%o2) [y > 0]

(%i3) ans2:atan2(y,x)+atan2(-y,x);

(%o3) atan2(y, x) + atan2(- y, x)

(%i4)

I also tried this on an older maxima on another box (unfortunately I left the version # at home) and things worked as expected.

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