atan2 - Online Linux Manual PageSection : 3
Updated : 2023-02-05
Source : Linux man-pages 6.03

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NAMEatan2, atan2f, atan2l − arc tangent function of two variables

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LIBRARYMath library (libm, −lm)

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SYNOPSIS#include <math.h>double atan2(double y, double x); float atan2f(float y, float x); long double atan2l(long double y, long double x);Feature 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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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DESCRIPTIONThese 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.

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RETURN VALUEOn success, these functions return the principal value of the arc tangent of y/x in radians; the return value is in the range [−pi, 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 −0, −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.

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ERRORSNo errors occur.

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ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7). InterfaceAttributeValue atan2(), atan2f(), atan2l() Thread safetyMT-Safe

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STANDARDSC99, POSIX.1-2001, POSIX.1-2008. The variant returning double also conforms to SVr4, 4.3BSD.

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SEE ALSOacos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3) 0

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