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

NAME
       atan, atanf, atanl - arc tangent function

SYNOPSIS
       #include <math.h>

       double atan(double x);
       float atanf(float x);
       long double atanl(long double x);

DESCRIPTION
       These 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 VALUE
       Upon successful completion, these functions shall return the arc tangent 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.

ERRORS
       These 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.

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
       atan2() , 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 Technology -- 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					  ATAN(P)
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