1FABS(3P)                   POSIX Programmer's Manual                  FABS(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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11

NAME

13       fabs, fabsf, fabsl — absolute value function
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SYNOPSIS

16       #include <math.h>
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18       double fabs(double x);
19       float fabsf(float x);
20       long double fabsl(long double x);
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DESCRIPTION

23       The functionality described on this reference page is aligned with  the
24       ISO C  standard.  Any  conflict between the requirements described here
25       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2008
26       defers to the ISO C standard.
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28       These  functions  shall  compute  the  absolute value of their argument
29       x,|x|.
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RETURN VALUE

32       Upon successful completion, these functions shall return  the  absolute
33       value of x.
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35       If x is NaN, a NaN shall be returned.
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37       If x is ±0, +0 shall be returned.
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39       If x is ±Inf, +Inf shall be returned.
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ERRORS

42       No errors are defined.
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44       The following sections are informative.
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EXAMPLES

47   Computing the 1-Norm of a Floating-Point Vector
48       This  example shows the use of fabs() to compute the 1-norm of a vector
49       defined as follows:
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51           norm1(v) = |v[0]| + |v[1]| + ... + |v[n−1]|
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53       where |x| denotes the absolute value  of  x,  n  denotes  the  vector's
54       dimension v[i] denotes the i-th component of v (0≤i<n).
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56           #include <math.h>
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58           double
59           norm1(const double v[], const int n)
60           {
61               int     i;
62               double  n1_v;  /* 1-norm of v */
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64               n1_v = 0;
65               for (i=0; i<n; i++) {
66                   n1_v += fabs (v[i]);
67               }
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69               return n1_v;
70           }
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APPLICATION USAGE

73       None.
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RATIONALE

76       None.
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FUTURE DIRECTIONS

79       None.
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SEE ALSO

82       isnan()
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84       The Base Definitions volume of POSIX.1‐2008, <math.h>
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87       Portions  of  this text are reprinted and reproduced in electronic form
88       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
89       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
90       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
91       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
92       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  In  the
93       event of any discrepancy between this version and the original IEEE and
94       The Open Group Standard, the original IEEE and The Open Group  Standard
95       is  the  referee document. The original Standard can be obtained online
96       at http://www.unix.org/online.html .
97
98       Any typographical or formatting errors that appear  in  this  page  are
99       most likely to have been introduced during the conversion of the source
100       files to man page format. To report such errors,  see  https://www.ker‐
101       nel.org/doc/man-pages/reporting_bugs.html .
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105IEEE/The Open Group                  2013                             FABS(3P)
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