trusty (3) atanf.3posix.gz

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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>


       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
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .