ATAN2(3P) POSIX Programmer's Manual ATAN2(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.NAMEatan2, atan2f, atan2l — arc tangent functionsSYNOPSIS#include <math.h> double atan2(double y, double x); float atan2f(float y, float x); long double atan2l(long double y, long double x);DESCRIPTIONThe functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2008 defers to the ISO C standard. These functions shall compute the principal value of the arc tangent of y/x, using the signs of both arguments to determine the quadrant of the return value. 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 y/x in the range [−π,π] radians. If y is ±0 and x is < 0, ±π shall be returned. If y is ±0 and x is > 0, ±0 shall be returned. If y is < 0 and x is ±0, −π/2 shall be returned. If y is > 0 and x is ±0, π/2 shall be returned. If x is 0, a pole error shall not occur. If either x or y is NaN, a NaN shall be returned. If the correct value would cause underflow, a range error may occur, and atan(), atan2f(), and atan2l() shall return an implementation- defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively. If the IEC 60559 Floating-Point option is supported, y/x should be returned. If y is ±0 and x is −0, ±π shall be returned. If y is ±0 and x is +0, ±0 shall be returned. For finite values of ±y > 0, if x is −Inf, ±π shall be returned. For finite values of ±y > 0, if x is +Inf, ±0 shall be returned. For finite values of x, if y is ±Inf, ±π/2 shall be returned. If y is ±Inf and x is −Inf, ±3π/4 shall be returned. If y is ±Inf and x is +Inf, ±π/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, 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.EXAMPLESConverting Cartesian to Polar Coordinates System The function below uses atan2() to convert a 2d vector expressed in cartesian coordinates (x,y) to the polar coordinates (rho,theta). There are other ways to compute the angle theta, using asin() acos(), or atan(). However, atan2() presents here two advantages: * The angle's quadrant is automatically determined. * The singular cases (0,y) are taken into account. Finally, this example uses hypot() rather than sqrt() since it is bet‐ ter for special cases; see hypot() for more information. #include <math.h> void cartesian_to_polar(const double x, const double y, double *rho, double *theta ) { *rho = hypot (x,y); /* better than sqrt(x*x+y*y) */ *theta =atan2(y,x); }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 ALSOacos(), asin(), atan(), feclearexcept(), fetestexcept(), hypot(), isnan(), sqrt(), tan() The Base Definitions volume of POSIX.1‐2008, Section 4.19, 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, 2013 Edition, Standard for Information TechnologyPortable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐ cal and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html . Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.ker‐ nel.org/doc/man-pages/reporting_bugs.html .--IEEE/The Open Group 2013 ATAN2(3P)

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