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 .