ATAN(3P) POSIX Programmer's Manual ATAN(3P)[top]PROLOGThis manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.NAMEatan, atanf, atanl - arc tangent functionSYNOPSIS#include <math.h> double atan(double x); float atanf(float x); long double atanl(long double x);DESCRIPTIONThese functions shall compute the principal value of the arc tangent of their argument x. An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.RETURN VALUEUpon successful completion, these functions shall return the arc tan‐ gent of x in the range [-pi/2,pi/2] radians. If x is NaN, a NaN shall be returned. If x is ±0, x shall be returned. If x is ±Inf, ±pi/2 shall be returned. If x is subnormal, a range error may occur and x should be returned.ERRORSThese functions may fail if: Range Error The value of x is subnormal. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised. The following sections are informative.EXAMPLESNone.APPLICATION USAGEOn error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.RATIONALENone.FUTURE DIRECTIONSNone.SEE ALSOatan2(), feclearexcept(), fetestexcept(), isnan(), tan(), the Base Def‐ initions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <math.h>COPYRIGHTPortions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information TechnologyPortable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .--IEEE/The Open Group 2003 ATAN(3P)

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