ATAN(3) Linux Programmer's Manual ATAN(3)[top]NAMEatan, atanf,atanl- arc tangent functionSYNOPSIS#include <math.h> double atan(double x); float atanf(float x); long double atanl( long double x); Link withFeature 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-lm.DESCRIPTIONThe atan() function calculates the principal value of the arc tangent of x; that is the value whose tangent is x.RETURN VALUEOn success, these functions return the principal value of the arc tan‐ gent 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.ERRORSNo errors occur.CONFORMING TOC99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD, C89.SEE ALSOacos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)COLOPHONThis page is part of release 3.54 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2010-09-20 ATAN(3)

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