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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 .