atanf(3) - f39

1atan(3)                    Library Functions Manual                    atan(3)
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NAME

6       atan, atanf, atanl - arc tangent function
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LIBRARY

9       Math library (libm, -lm)
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SYNOPSIS

12       #include <math.h>
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14       double atan(double x);
15       float atanf(float x);
16       long double atanl(long double x);
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18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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20       atanf(), atanl():
21           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
22               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
23               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

26       These  functions calculate the principal value of the arc tangent of x;
27       that is the value whose tangent is x.
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RETURN VALUE

30       On success, these functions return the principal value of the arc  tan‐
31       gent of x in radians; the return value is in the range [-pi/2, pi/2].
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33       If x is a NaN, a NaN is returned.
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35       If x is +0 (-0), +0 (-0) is returned.
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37       If  x  is  positive  infinity (negative infinity), +pi/2 (-pi/2) is re‐
38       turned.
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ERRORS

41       No errors occur.
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ATTRIBUTES

44       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
45       tributes(7).
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47       ┌────────────────────────────────────────────┬───────────────┬─────────┐
48       │Interface                                   │ Attribute     │ Value   │
49       ├────────────────────────────────────────────┼───────────────┼─────────┤
50       │atan(), atanf(), atanl()                    │ Thread safety │ MT-Safe │
51       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

54       C11, POSIX.1-2008.
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HISTORY

57       C99, POSIX.1-2001.
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59       The variant returning double also conforms to SVr4, 4.3BSD, C89.
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