Format

      #include  <math.h>

      double atan  (double x);

      float atanf  (float x); (Integrity servers, Alpha)

      long double atanl  (long double x); (Integrity servers, Alpha)

      double atand  (double x); (Integrity servers, Alpha)

      float atandf  (float x); (Integrity servers, Alpha)

      long double atandl  (long double x);

                          (Integrity servers, Alpha)

1 - Argument

 x

    A radian expressed as a real number.

2 - Description

    The atan functions compute the principal value of the arc tangent
    of x in the range [-pi/2,pi/2] radians.

    The atand functions compute the principal value of the arc
    tangent of x in the range [-90,90] degrees.