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+'\" et
+.TH FABS "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
+.\"
+.SH 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.
+.\"
+.SH NAME
+fabs,
+fabsf,
+fabsl
+\(em absolute value function
+.SH SYNOPSIS
+.LP
+.nf
+#include <math.h>
+.P
+double fabs(double \fIx\fP);
+float fabsf(float \fIx\fP);
+long double fabsl(long double \fIx\fP);
+.fi
+.SH 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\(hy2017 defers to the ISO\ C standard.
+.P
+These functions shall compute the absolute value of their argument
+.IR x ,|\c
+.IR x |.
+.SH "RETURN VALUE"
+Upon successful completion, these functions shall return the absolute
+value of
+.IR x .
+.P
+If
+.IR x
+is NaN, a NaN shall be returned.
+.P
+If
+.IR x
+is \(+-0, +0 shall be returned.
+.P
+If
+.IR x
+is \(+-Inf, +Inf shall be returned.
+.SH ERRORS
+No errors are defined.
+.LP
+.IR "The following sections are informative."
+.SH EXAMPLES
+.SS "Computing the 1-Norm of a Floating-Point Vector"
+.P
+This example shows the use of
+\fIfabs\fR()
+to compute the 1-norm of a vector defined as follows:
+.sp
+.RS 4
+.nf
+
+norm1(v) = |v[0]| + |v[1]| + ... + |v[n-1]|
+.fi
+.P
+.RE
+.P
+where |\fIx\fR| denotes the absolute value of \fIx\fR, \fIn\fR denotes
+the vector's dimension \fIv\fR[\fIi\fR] denotes the
+.IR i -th
+component of \fIv\fR (0\(<=\fIi\fR<\fIn\fR).
+.sp
+.RS 4
+.nf
+
+#include <math.h>
+.P
+double
+norm1(const double v[], const int n)
+{
+    int     i;
+    double  n1_v;  /* 1-norm of v */
+.P
+    n1_v = 0;
+    for (i=0; i<n; i++) {
+        n1_v += fabs (v[i]);
+    }
+.P
+    return n1_v;
+}
+.fi
+.P
+.RE
+.SH "APPLICATION USAGE"
+None.
+.SH RATIONALE
+None.
+.SH "FUTURE DIRECTIONS"
+None.
+.SH "SEE ALSO"
+.IR "\fIisnan\fR\^(\|)"
+.P
+The Base Definitions volume of POSIX.1\(hy2017,
+.IR "\fB<math.h>\fP"
+.\"
+.SH COPYRIGHT
+Portions of this text are reprinted and reproduced in electronic form
+from IEEE Std 1003.1-2017, Standard for Information Technology
+-- Portable Operating System Interface (POSIX), The Open Group Base
+Specifications Issue 7, 2018 Edition,
+Copyright (C) 2018 by the Institute of
+Electrical and Electronics Engineers, Inc and The Open Group.
+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.opengroup.org/unix/online.html .
+.PP
+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 .