
atan(+Y, +X, -Result)
-Result is atan(+Y, +X)

   Computes the arc tangent function of two variables and unifies the resulting value with Result.

Arguments
   Y                   A number.
   X                   A number.
   Result              Output: float or breal.

Type
   Arithmetic

Description

   Computes the arc tangent function of two variables and unifies the
   resulting value with Result.

    It is similar to calculating the arc tangent of Y/X, except that the
    signs of both arguments are used to determine the quadrant of the result.
    The result lies in the interval -pi..pi. The operation is valid even if
    X is zero, in which case the result is pi/2 or -pi/2.  One application
    is the conversion of cartesian to polar coordinates, where this function
    computes the angle component (in radians).

   This predicate can be used as a function in arithmetic expressions.
   In coroutining mode, if X or Y is uninstantiated, the call to atan/3 is
   delayed until both variables are instantiated.




Modes and Determinism
   atan(+, +, -) is det

Exceptions
     4 --- X or Y is not instantiated (non-coroutining mode only).
    24 --- Number is not of a numeric type.

Examples
   
Success:
    Result is atan( 0.0, -1.0).		% gives Result =  3.141592
    Result is atan( 1.0, -1.0).		% gives Result =  2.356194
    Result is atan( 1.0,  0.0).		% gives Result =  1.570796
    Result is atan( 1.0,  1.0).		% gives Result =  0.785398
    Result is atan( 0.0,  0.0).		% gives Result =  0.0
    Result is atan(-1.0,  1.0).		% gives Result = -0.785398
    Result is atan(-1.0,  0.0).		% gives Result = -1.570796
    Result is atan(-1.0, -1.0).		% gives Result = -2.356194
    Result is atan(-0.0, -1.0).		% gives Result = -3.141592

    Result is atan( 7.0,  7.0).		% gives Result =  0.785398


See Also
   is / 2
