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+.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
+.\" Distributed under GPL
+.\" Based on glibc infopages
+.\"
+.\" Corrections by aeb
+.TH  NAN 3 2002-08-10 "GNU" "libc math functions"
+.SH NAME
+nan, nanf, nanl \- return 'Not a Number'
+.SH SYNOPSIS
+.B #include <math.h>
+.sp
+.BI "double nan(const char *" tagp );
+.sp
+.BI "float nanf(const char *" tagp );
+.sp
+.BI "long double nanl(const char *" tagp );
+.sp
+Link with \-lm.
+.SH DESCRIPTION
+These functions return a representation (determined by
+.IR tagp )
+of a quiet NaN. If the implementation does not support
+quiet NaNs, these functions return zero.
+.LP
+The call
+.I nan("char-sequence")
+is equivalent to 
+.I strtod ("NAN(char-sequence)",NULL)
+and similarly calls to
+.I nanf
+and
+.I nanl
+are equivalent to analogous calls to
+.I strtof
+and
+.IR strtold .
+.PP
+The argument
+.I tagp
+is used in an unspecified manner.  On IEEE 754 systems, there are
+many representations of NaN, and
+.I tagp
+selects one.  On other systems it may do nothing.
+.SH "CONFORMING TO"
+C99. See also IEC 559 and the appendix with
+recommended functions in IEEE 754/IEEE 854.
+.SH "SEE ALSO"
+.BR isnan (3),
+.BR strtod (3)