1TAN(P)                     POSIX Programmer's Manual                    TAN(P)
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NAME

6       tan, tanf, tanl - tangent function
7

SYNOPSIS

9       #include <math.h>
10
11       double tan(double x);
12       float tanf(float x);
13       long double tanl(long double x);
14
15

DESCRIPTION

17       These functions shall compute the tangent of their argument x, measured
18       in radians.
19
20       An application wishing to check for error situations should  set  errno
21       to  zero  and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
22       functions.  On return, if errno is non-zero or  fetestexcept(FE_INVALID
23       |  FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
24       occurred.
25

RETURN VALUE

27       Upon successful completion, these functions shall return the tangent of
28       x.
29
30       If the correct value would cause underflow, and is not representable, a
31       range error may occur, and    either 0.0 (if supported), or   an imple‐
32       mentation-defined value shall be returned.
33
34       If x is NaN, a NaN shall be returned.
35
36       If x is ±0, x shall be returned.
37
38       If x is subnormal, a range error may occur and x should be returned.
39
40       If  x  is  ±Inf,  a domain error shall occur, and either a NaN (if sup‐
41       ported), or an implementation-defined value shall be returned.
42
43       If the correct value would cause underflow,  and  is  representable,  a
44       range error may occur and the correct value shall be returned.
45
46       If  the  correct  value would cause overflow, a range error shall occur
47       and tan(), tanf(), and tanl() shall return ±HUGE_VAL,  ±HUGE_VALF,  and
48       ±HUGE_VALL,  respectively,  with  the same sign as the correct value of
49       the function.
50

ERRORS

52       These functions shall fail if:
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54       Domain Error
55              The value of x is ±Inf.
56
57       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
58       then   errno  shall  be  set  to  [EDOM].  If  the  integer  expression
59       (math_errhandling &  MATH_ERREXCEPT)  is  non-zero,  then  the  invalid
60       floating-point exception shall be raised.
61
62       Range Error
63              The result overflows
64
65       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
66       then errno  shall  be  set  to  [ERANGE].  If  the  integer  expression
67       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero,  then the overflow
68       floating-point exception shall be raised.
69
70
71       These functions may fail if:
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73       Range Error
74              The result underflows,    or the value of x is subnormal.
75
76       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
77       then  errno  shall  be  set  to  [ERANGE].  If  the  integer expression
78       (math_errhandling & MATH_ERREXCEPT) is  non-zero,  then  the  underflow
79       floating-point exception shall be raised.
80
81
82       The following sections are informative.
83

EXAMPLES

85   Taking the Tangent of a 45-Degree Angle
86              #include <math.h>
87              ...
88              double radians = 45.0 * M_PI / 180;
89              double result;
90              ...
91              result = tan (radians);
92

APPLICATION USAGE

94       There  are no known floating-point representations such that for a nor‐
95       mal argument, tan( x) is either overflow or underflow.
96
97       These functions may lose accuracy when their argument is near a  multi‐
98       ple of pi/2 or is far from 0.0.
99
100       On   error,   the   expressions  (math_errhandling  &  MATH_ERRNO)  and
101       (math_errhandling & MATH_ERREXCEPT) are independent of each other,  but
102       at least one of them must be non-zero.
103

RATIONALE

105       None.
106

FUTURE DIRECTIONS

108       None.
109

SEE ALSO

111       atan()  , feclearexcept() , fetestexcept() , isnan() , the Base Defini‐
112       tions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of  Error
113       Conditions for Mathematical Functions, <math.h>
114

116       Portions  of  this text are reprinted and reproduced in electronic form
117       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
118       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
119       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
120       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
121       event of any discrepancy between this version and the original IEEE and
122       The  Open Group Standard, the original IEEE and The Open Group Standard
123       is the referee document. The original Standard can be  obtained  online
124       at http://www.opengroup.org/unix/online.html .
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128IEEE/The Open Group                  2003                               TAN(P)
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