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+'\" et
+.TH ERF "3P" 2013 "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.
+
+.EQ
+delim $$
+.EN
+.SH NAME
+erf,
+erff,
+erfl
+\(em error functions
+.SH SYNOPSIS
+.LP
+.nf
+#include <math.h>
+.P
+double erf(double \fIx\fP);
+float erff(float \fIx\fP);
+long double erfl(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\(hy2008 defers to the ISO\ C standard.
+.P
+These functions shall compute the error function of their argument
+.IR x ,
+defined as:
+.sp
+.RS
+${2 over sqrt pi} int from 0 to x e"^" " "{- t"^" 2" "} dt$
+.RE
+.P
+An application wishing to check for error situations should set
+.IR errno
+to zero and call
+.IR feclearexcept (FE_ALL_EXCEPT)
+before calling these functions. On return, if
+.IR errno
+is non-zero or \fIfetestexcept\fR(FE_INVALID | FE_DIVBYZERO |
+FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
+.SH "RETURN VALUE"
+Upon successful completion, these functions shall return the value of
+the error function.
+.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, \(+-1 shall be returned.
+.P
+If the correct value would cause underflow, a range error may occur, and
+\fIerf\fR(),
+\fIerff\fR(),
+and
+\fIerfl\fR()
+shall return an implementation-defined value no greater in magnitude
+than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.
+.P
+If the IEC 60559 Floating-Point option is supported, 2 *
+.IR x /\c
+.IR sqrt (\(*p)
+should be returned.
+.SH ERRORS
+These functions may fail if:
+.IP "Range\ Error" 12
+The result underflows.
+.RS 12 
+.P
+If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
+non-zero, then
+.IR errno
+shall be set to
+.BR [ERANGE] .
+If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
+non-zero, then the underflow floating-point exception shall be raised.
+.RE
+.br
+.LP
+.IR "The following sections are informative."
+.SH EXAMPLES
+.SS "Computing the Probability for a Normal Variate"
+.P
+This example shows how to use
+\fIerf\fR()
+to compute the probability that a normal variate assumes a value in the
+range [\fIx\fR1,\fIx\fR2] with \fIx\fR1\(<=\fIx\fR2.
+.P
+This example uses the constant M_SQRT1_2 which is part of the XSI option.
+.sp
+.RS 4
+.nf
+\fB
+#include <math.h>
+.P
+double
+Phi(const double x1, const double x2)
+{
+    return ( erf(x2*M_SQRT1_2) \(mi erf(x1*M_SQRT1_2) ) / 2;
+}
+.fi \fR
+.P
+.RE
+.SH "APPLICATION USAGE"
+Underflow occurs when |\fIx\fP| < DBL_MIN * (\c
+.IR sqrt (\(*p)/2).
+.P
+On error, the expressions (\fImath_errhandling\fR & MATH_ERRNO) and
+(\fImath_errhandling\fR & MATH_ERREXCEPT) are independent of each
+other, but at least one of them must be non-zero.
+.SH RATIONALE
+None.
+.SH "FUTURE DIRECTIONS"
+None.
+.SH "SEE ALSO"
+.IR "\fIerfc\fR\^(\|)",
+.IR "\fIfeclearexcept\fR\^(\|)",
+.IR "\fIfetestexcept\fR\^(\|)",
+.IR "\fIisnan\fR\^(\|)"
+.P
+The Base Definitions volume of POSIX.1\(hy2008,
+.IR "Section 4.19" ", " "Treatment of Error Conditions for Mathematical Functions",
+.IR "\fB<math.h>\fP"
+.SH 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 .