atan(3) Library Functions Manual atan(3) NAME atan, atanf, atanl - arc tangent function LIBRARY Math library (libm, -lm) SYNOPSIS #include double atan(double x); float atanf(float x); long double atanl(long double x); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): atanf(), atanl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE 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 | +--------------------------------------------+---------------+---------+ STANDARDS C11, POSIX.1-2008. HISTORY C99, POSIX.1-2001. 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) Linux man-pages 6.9.1 2024-05-02 atan(3)