9.3.19 ATAN2 (Y, X)

Description:  Produces an arctangent. The result is the principal value of the argument of the nonzero complex number (X, Y). 
Class:  Elemental function; Generic 
Arguments:  Y   Must be of type real. 
  X   Must have the same type and kind parameters as Y. If Y has the value zero, X cannot have the value zero. 
Results:  The result type is the same as X and is expressed in radians. The value lies in the range -pi < ATAN2 (Y, X) <= pi. If X /= zero, the result is approximately equal to the value of arctan (Y/X).

If Y > zero, the result is positive.

If Y < zero, the result is negative.

If Y = zero, the result is zero (if X > zero) or pi (if X < zero).

If X = zero, the absolute value of the result is pi/2. 

Specific Name  Argument Type  Result Type 
ATAN2  REAL(4)  REAL(4) 
QATAN2  REAL(16)  REAL(16) 


ATAN2 (2.679676, 1.0) has the value 1.213623.

If Y has the value

  [  1   1 ]
  [ -1  -1 ]
and X has the value
  [ -1  1 ]
  [ -1  1 ],
then ATAN2 (Y, X) is

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