ATAN(3) - man page online | library functions

Arc tangent function.

ATAN(3)                             Linux Programmer's Manual                             ATAN(3)

NAME atan, atanf, atanl - arc tangent function
SYNOPSIS #include <math.h> double atan(double x); float atanf(float x); long double atanl( long double x); Link with -lm. Feature Test Macro Requirements for glibc (see feature_test_macros(7)): atanf(), atanl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99
DESCRIPTION These functions calculate the principal value of the arc tangent of x; that is the value whose tangent is x.
RETURN VALUE On success, these functions return the principal value of the arc tangent of x in radians; the return value is in the range [-pi/2, pi/2]. If x is a NaN, a NaN is returned. If x is +0 (-0), +0 (-0) is returned. If x is positive infinity (negative infinity), +pi/2 (-pi/2) is returned.
ERRORS No errors occur.
ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌─────────────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├─────────────────────────┼───────────────┼─────────┤ │atan(), atanf(), atanl() │ Thread safety │ MT-Safe │ └─────────────────────────┴───────────────┴─────────┘
CONFORMING TO C99, POSIX.1-2001, POSIX.1-2008. The variant returning double also conforms to SVr4, 4.3BSD, C89.
SEE ALSO acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)
COLOPHON This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at
2015-04-19 ATAN(3)
This manual Reference Other manuals
atan(3) referred by acos(3) | asin(3) | atan2(3) | cos(3) | sin(3) | tan(3)
refer to acos(3) | asin(3) | atan2(3) | attributes(7) | carg(3) | catan(3) | cos(3) | feature_test_macros(7) | sin(3) | tan(3)