# atan(3) [minix man page]

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

atan, 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(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE-lm.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 4.15 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 https://www.kernel.org/doc/man-pages/. 2017-09-15 ATAN(3)

## Check Out this Related Man Page

ATAN2(3) Linux Programmer's Manual ATAN2(3)NAME

atan2, atan2f, atan2l - arc tangent function of two variablesSYNOPSIS

#include <math.h> double atan2(double y, double x); float atan2f(float y, float x); long double atan2l(long double y, long double x); Link withFeature Test Macro Requirements for glibc (see feature_test_macros(7)): atan2f(), atan2l(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE-lm.DESCRIPTION

These functions calculate the principal value of the arc tangent of y/x, using the signs of the two arguments to determine the quadrant of the result.RETURN VALUE

On success, these functions return the principal value of the arc tangent of y/x in radians; the return value is in the range [, pi]. If y is +0 (-0) and x is less than 0, +pi (-pi) is returned. If y is +0 (-0) and x is greater than 0, +0 (-0) is returned. If y is less than 0 and x is +0 or-pi, -pi/2 is returned. If y is greater than 0 and x is +0 or-0, pi/2 is returned. If either x or y is NaN, a NaN is returned. If y is +0 (-0) and x is-0, +pi (-pi) is returned. If y is +0 (-0) and x is +0, +0 (-0) is returned. If y is a finite value greater (less) than 0, and x is negative infinity, +pi (-pi) is returned. If y is a finite value greater (less) than 0, and x is positive infinity, +0 (-0) is returned. If y is positive infinity (negative infinity), and x is finite, pi/2 (-pi/2) is returned. If y is positive infinity (negative infinity) and x is negative infinity, +3*pi/4 (-3*pi/4) is returned. If y is positive infinity (negative infinity) and x is positive infinity, +pi/4 (-pi/4) is returned.-0ERRORS

No errors occur.ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7). +-----------------------------+---------------+---------+ |Interface | Attribute | Value | +-----------------------------+---------------+---------+ |atan2(), atan2f(), atan2l() | 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), atan(3), carg(3), cos(3), sin(3), tan(3)COLOPHON

This page is part of release 4.15 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 https://www.kernel.org/doc/man-pages/. 2017-09-15 ATAN2(3)