ATAN(3)                   (2017-09-15)                    ATAN(3)

     NAME
          atan, atanf, atanl - arc tangent function

     SYNOPSIS
          #include <math.h>

          double atan(double x);
          float atanf(float x);
          long double atanl( long double x);

          Link with -lm.

     Feature Test Macro Requirements for glibc (see
     feature_test_macros(7)):

          atanf(), atanl():
              _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
                  || /* Since glibc 2.19: */ _DEFAULT_SOURCE
                  || /* Glibc versions <= 2.19: */ _BSD_SOURCE ||
              _SVID_SOURCE

     DESCRIPTION
          These functions calculate the principal  value  of  the  arc
          tangent of x; that is the value whose tangent is x.

     RETURN VALUE
          On success, these functions return the  principal  value  of
          the  arc tangent of x in radians; the return value is in the
          range [-pi/2, pi/2].

          If x is a NaN, a NaN is returned.

          If x is +0 (-0), +0 (-0) is returned.

          If x is positive infinity (negative infinity), +pi/2 (-pi/2)
          is returned.

     ERRORS
          No errors occur.

     ATTRIBUTES
          For an explanation of the terms used in  this  section,  see
          attributes(7).     allbox;    lbw24    lb    lb   l   l   l.
          Interface Attribute Value  T{   atan(),   atanf(),   atanl()
          T}   Thread safety  MT-Safe

     CONFORMING TO
          C99, POSIX.1-2001, POSIX.1-2008.

          The variant returning double also conforms to SVr4,  4.3BSD,

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     ATAN(3)                   (2017-09-15)                    ATAN(3)

          C89.

     SEE ALSO
          acos(3),  asin(3),  atan2(3),  carg(3),  catan(3),   cos(3),
          sin(3), tan(3)

     COLOPHON
          This page is part of release 5.10  of  the  Linux  man-pages
          project.   A  description  of the project, information about
          reporting bugs, and the latest version of this page, can  be
          found at https://www.kernel.org/doc/man-pages/.

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