NAME

       tan, tanf, tanl - tangent function

SYNOPSIS

       #include <math.h>

       double tan(double x);
       float tanf(float x);
       long double tanl(long double x);

DESCRIPTION

       These functions shall compute the tangent of their argument x, measured in radians.

       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 tangent of x.

       If  the  correct  value  would  cause  underflow,  and is not representable, a range error may occur, and
        either 0.0 (if supported), or   an implementation-defined value shall be returned.

       If x is NaN, a NaN shall be returned.

       If x is ±0, x shall be returned.

       If x is subnormal, a range error may occur and x should be returned.

       If x is ±Inf, a domain error shall occur, and either a NaN (if supported), or  an  implementation-defined
       value shall be returned.

       If the correct value would cause underflow, and is representable, a range error may occur and the correct
       value shall be returned.

       If  the correct value would cause overflow, a range error shall occur and tan(), tanf(), and tanl() shall
       return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively, with the same sign as the  correct  value  of
       the function.

ERRORS

       These functions shall fail if:

       Domain Error
              The value of x is ±Inf.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM].
       If  the  integer  expression  (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-
       point exception shall be raised.

       Range Error
              The result overflows

       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 overflow
       floating-point exception shall be raised.

       These functions may fail if:

       Range Error
              The result underflows,    or 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

   Taking the Tangent of a 45-Degree Angle
              #include <math.h>
              ...
              double radians = 45.0 * M_PI / 180;
              double result;
              ...
              result = tan (radians);

APPLICATION USAGE

       There are no known floating-point representations such that for a normal  argument,  tan(  x)  is  either
       overflow or underflow.

       These functions may lose accuracy when their argument is near a multiple of pi/2 or is far from 0.0.

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

IEEE/The Open Group                                   2003                                                TAN(P)