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TAN(3P)                    POSIX Programmer's Manual                   TAN(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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 implemen-
       tation-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  sup-
       ported), 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  nor-
       mal argument, tan( x) is either overflow or underflow.
       These  functions may lose accuracy when their argument is near a multi-
       ple 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 Condi-
       tions 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(3P)