atan(3I)

NAME
     ATAN, DATAN, QATAN, ATAND, DATAND, QATAND - Computes arctangent
     (inverse tangent) for single argument

SYNOPSIS
     ATAN ([X=]x)
     DATAN ([X=]x)
     QATAN ([X=]x)

     ATAND ([X=]x)
     DATAND ([X=]x)
     QATAND ([X=]x)

STANDARDS
     Fortran

     Fortran extensions:  QATAN, ATAND, DATAND, QATAND

DESCRIPTION
     ATAN, DATAN, and QATAN return the arc tangent in radians.  ATAND,
     DATAND, and QATAND return the arc tangent in degrees.

     ATAN and ATAND are generic function names; the others are specifics.
     These are elemental intrinsic functions.  They accept the following
     argument:

     x         Must be type real.  The type and kind type of x is identical
               to the type and kind type of the return value.  See the
               RETURN VALUES section for information on input data types
               and return values.

               The terms single precision, double precision, and quad
               precision differ depending on your platform.  For
               platform-specific information, see the TERMINOLOGY section
               of the INTRO_INTRIN(3I) man page.

     These functions evaluate y = arctan(x).

     The result range for ATAN, DATAN, and QATAN is -pi/2 <= ATAN(x) <=
     pi/2.

     The result range for ATAND, DATAND, and QATAND is -90 <= result <= 90.

     A vector version of the single-precision and double-precision ATAN
     intrinsic exists on IRIX systems and is used when -O3 is specified on
     the compiler command line.

NOTES
     The ATAN and DATAN intrinsic function names can be passed as
     arguments; the others cannot.

RETURN VALUES
     ATAN and ATAND return the real arc tangent of their real arguments.

     DATAN and DATAND return the double-precision arc tangent of their
     double-precision arguments.

     QATAN and QATAND return the quad-precision arc tangent of their
     quad-precision arguments.