atan2f(3) [posix man page]

ATAN2(P)						     POSIX Programmer's Manual							  ATAN2(P)

NAME

       atan2, atan2f, atan2l - arc tangent functions

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);

DESCRIPTION

       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 VALUE

       Upon successful completion, these functions shall return the arc tangent of y/ x in the range [-pi,pi] radians.

       If y is +-0 and x is < 0, +-pi shall be returned.

       If y is +-0 and x is > 0, +-0 shall be returned.

       If y is < 0 and x is +-0, -pi/2 shall be returned.

       If y is > 0 and x is +-0, pi/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 result underflows, a range error may occur and y/ x should be returned.

       If y is +-0 and x is -0, +-pi 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, +-pi 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, +-pi/2 shall be returned.

       If y is +-Inf and x is -Inf, +-3pi/4 shall be returned.

       If y is +-Inf and x is +Inf, +-pi/4 shall be returned.

       If both arguments are 0, a domain error shall not occur.

ERRORS

       These 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.

EXAMPLES

       None.

APPLICATION USAGE

       On  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.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       atan() , 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>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable 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								  ATAN2(P)