atan2 -- compute an angle of a certain triangle

• Usage:

  atan2(y,x)

  atan2(y,I)

  atan2(J,x)

  atan2(J,I)

• Inputs:
  • y, a real number
  • x, a real number
  • J, a real interval
  • I, a real interval
• Outputs:
  • a real number, the angle (in radians) formed with the x-axis by the ray from the origin to the point (x,y)
  • a real number, an interval containing the angles (in radians) formed with the x-axis by the rays from the origin to the points of (I,y),(x,J),(I,J)

i1 : atan2(1,0)

o1 = 1.570796326794897

o1 : RR (of precision 53)

i2 : atan2(0,1)

o2 = 0

o2 : RR (of precision 53)

i3 : atan2(-1,-1)

o3 = -2.356194490192345

o3 : RR (of precision 53)