atan2

Returns the angle theta of the polar coordinates (r, theta) that correspond to the rectangular coordinates (x, y) by computing the arc tangent of the value y / x; the returned value is an angle in the range from -PI to PI radians.

Special cases:

• atan2(0.0, 0.0) is 0.0
• atan2(0.0, x) is 0.0 for x > 0 and PI for x < 0
• atan2(-0.0, x) is -0.0 for 'x > 0 and -PI for x < 0`
• atan2(y, +Inf) is 0.0 for 0 < y < +Inf and -0.0 for '-Inf < y < 0`
• atan2(y, -Inf) is PI for 0 < y < +Inf and -PI for -Inf < y < 0
• atan2(y, 0.0) is PI/2 for y > 0 and -PI/2 for y < 0
• atan2(+Inf, x) is PI/2 for finite xy
• atan2(-Inf, x) is -PI/2 for finite x
• atan2(NaN, x) and atan2(y, NaN) is NaN