Four quadrant inverse tangens (select solution that is closest to given angle y0)
This function returns y = atan3(u1,u2,y0) such that
tan(y) = u1/u2 and
y is in the range: -pi < y-y0 < pi.
u2 may be zero, provided u1 is not zero. The difference to Modelica.Math.atan2(..) is the optional third argument y0 that allows to specify which of the infinite many solutions shall be returned: