HP-UX Reference (11i v1 05/09) - 3 Library Functions A-M (vol 6)

atan(3M) atan(3M)

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 speci-

fying -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.