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)

IMPLEMENTATION
     UNICOS, UNICOS/mk, IRIX systems

     CF90, MIPSpro 7 Fortran 90, MIPSpro Fortran 77

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 data type and kind type for single-precision,
               double-precision, and quad-precision values 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 as follows:

          -pi/2 <= ATAN(x) <= pi/2

     The result range for ATAND, DATAND, and QATAND is as follows:

          -90 <= result <= 90

     Vector versions of these intrinsics exist on some systems.  Vector
     versions of ATAN and DATAN exist on UNICOS and UNICOS/mk systems.  On
     UNICOS/mk systems, the vector versions of these intrinsics are used
     when -O vector3 or -O3 have been specified on the compiler command
     line.  On UNICOS/mk systems, the 64-bit intrinsic vectorizes; the
     32-bit version does not.  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.

     On CRAY T90 systems that support IEEE arithmetic, the following return
     values occur:

          ATAN(NaN) = NaN

          ATAN(infinity) = pi/2

          ATAN(-infinity) = -pi/2

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.

SEE ALSO
     Intrinsic Procedures Reference Manual for the printed version of this
     man page.