focal (3) fabs.3posix.gz

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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
       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 a 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>


       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 .