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ATAN2(3P) POSIX Programmer's Manual ATAN2(3P)PROLOGThis manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may dif- fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.NAMEatan2, atan2f, atan2l - arc tangent functionsSYNOPSIS#include<math.h>doubleatan2(doubley,doublex);floatatan2f(floaty,floatx);longdoubleatan2l(longdoubley,longdoublex);DESCRIPTIONThese functions shall compute the principal value of the arc tangent ofy/x, using the signs of both arguments to determine the quadrant of the return value. An application wishing to check for error situations should seterrnoto zero and callfeclearex-cept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.RETURNVALUEUpon successful completion, these functions shall return the arc tangent ofy/xin the range [-pi,pi] radians. Ifyis ?0 andxis < 0, ?pi shall be returned. Ifyis ?0 andxis > 0, ?0 shall be returned. Ifyis < 0 andxis ?0, -pi/2 shall be returned. Ifyis > 0 andxis ?0, pi/2 shall be returned. Ifxis 0, a pole error shall not occur. If eitherxoryis NaN, a NaN shall be returned. If the result underflows, a range error may occur andy/xshould be returned. Ifyis ?0 andxis -0, ?pi shall be returned. Ifyis ?0 andxis +0, ?0 shall be returned. For finite values of ?y> 0, ifxis -Inf, ?pi shall be returned. For finite values of ?y> 0, ifxis +Inf, ?0 shall be returned. For finite values ofx, ifyis ?Inf, ?pi/2 shall be returned. Ifyis ?Inf andxis -Inf, ?3pi/4 shall be returned. Ifyis ?Inf andxis +Inf, ?pi/4 shall be returned. If both arguments are 0, a domain error shall not occur.ERRORSThese functions may fail if: Range Error The result underflows. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, thenerrnoshall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.Thefollowingsectionsareinformative.EXAMPLESNone.APPLICATIONUSAGEOn error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are indepen- dent of each other, but at least one of them must be non-zero.RATIONALENone.FUTUREDIRECTIONSNone.SEEALSOatan(),feclearexcept(),fetestexcept(),isnan(),tan(), the Base Definitions 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, Stan- dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica- tions 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 Stan- dard, 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 ATAN2(3P)