NAME
atan(), atanf() — arctangent functions
SYNOPSIS
#include <math.h>
double atan(double x);
float atanf(float x);
DESCRIPTION
atan()
returns the arctangent of
x
in the range -π/2 to π/2.
atanf()
is a
float
version of
atan();
it takes a
float
argument and returns a
float
result.
To use this function, compile either with the default
-Ae
option or with the
-Aa
and
-D_HPUX_SOURCE
options.
atanf()
is not specified by any standard, but
it is named in accordance with the conventions
specified in the "Future Library Directions" section of the
ANSI C standard.
To use these functions, make sure your program includes
<math.h>,
and link in the math library by specifying
-lm
on the compiler or linker command line.
Millicode versions of the
atan()
function are available.
Millicode versions of math library functions are usually
faster than their counterparts in the standard library.
To use these versions, compile your program with the
+Olibcalls
or the
+Oaggressive
optimization option.
For special cases, the millicode versions return the same values as
their standard library counterparts (see the
RETURN VALUE
section).
For more information, see the
HP-UX Floating-Point Guide.
RETURN VALUE
If
x
is ±INFINITY,
atan()
returns ±π/2 respectively.
If
x
is NaN,
atan()
returns NaN.
If the correct value after rounding would be smaller in magnitude than
MINDOUBLE,
atan()
returns zero.
ERRORS
No errors are defined.
STANDARDS CONFORMANCE
atan(): SVID3, XPG4.2, ANSI C
