FABS(3)                    POSIX Programmer's Manual                   FABS(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.


NAME
       fabs, fabsf, fabsl -- absolute value function

SYNOPSIS
       #include <math.h>

       double fabs(double _x);
       float fabsf(float _x);
       long double fabsl(long double _x);

DESCRIPTION
       The functionality described on this reference page is aligned with the
       ISO C standard. Any conflict between the requirements described here
       and the ISO C standard is unintentional. This volume of POSIX.1-2008
       defers to the ISO C standard.

       These functions shall compute the absolute value of their argument
       _x,|_x|.

RETURN VALUE
       Upon successful completion, these functions shall return the absolute
       value of _x.

       If _x is NaN, a NaN shall be returned.

       If _x is +-0, +0 shall be returned.

       If _x is +-Inf, +Inf shall be returned.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
   Computing the 1-Norm of aa Floating-Point Vector
       This example shows the use of fabs() to compute the 1-norm of a vector
       defined as follows:

           norm1(v) == |v[0]| ++ |v[1]| ++ ...... ++ |v[n-1]|

       where |_x| denotes the absolute value of _x, _n denotes the vector's
       dimension _v[_i] denotes the _i-th component of _v (0<=_i<_n).

           #include <math.h>

           double
           norm1(const double v[], const int n)
           {
               int     i;
               double  n1_v;  /* 1-norm of v */

               n1_v = 0;
               for (i=0; i<n; i++) {
                   n1_v += fabs (v[i]);
               }

               return n1_v;
           }

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       isnan()

       The Base Definitions volume of POSIX.1-2008, <math.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2013                              FABS(3)
