man3/erf.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
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  14 .\" Since the Linux kernel and libraries are constantly changing, this
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  22 .\" Formatted or processed versions of this manual, if unaccompanied by
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  24 .\"
  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  30 .\" Modified 2002-07-27 by Walter Harms
  31 .\"     (walter.harms@informatik.uni-oldenburg.de)
  32 .\"
  33 .TH ERF 3  2010-09-20 "GNU" "Linux Programmer's Manual"
  34 .SH NAME
  35 erf, erff, erfl, \- error function
  36 .SH SYNOPSIS
  37 .nf
  38 .B #include <math.h>
  39
  40 .BI "double erf(double " x );
  41 .BI "float erff(float " x );
  42 .BI "long double erfl(long double " x );
  43
  44 .fi
  45 Link with \fI\-lm\fP.
  46 .sp
  47 .in -4n
  48 Feature Test Macro Requirements for glibc (see
  49 .BR feature_test_macros (7)):
  50 .in
  51 .sp
  52 .ad l
  53 .BR erf ():
  54 .RS 4
  55 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE ||
  56 _POSIX_C_SOURCE\ >=\ 200112L;
  57 .br
  58 or
  59 .I cc\ -std=c99
  60 .RE
  61 .br
  62 .BR erff (),
  63 .BR erfl ():
  64 .RS 4
  65 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
  66 _POSIX_C_SOURCE\ >=\ 200112L;
  67 .br
  68 or
  69 .I cc\ -std=c99
  70 .RE
  71 .ad b
  72 .SH DESCRIPTION
  73 The
  74 .BR erf ()
  75 function returns the error function of \fIx\fP, defined
  76 as
  77 .TP
  78     erf(x) = 2/sqrt(pi)* integral from 0 to x of exp(\-t*t) dt
  79 .SH RETURN VALUE
  80 On success, these functions return the error function of
  81 .IR x ,
  82 a value in the range [\-1,\ 1].
  83
  84 If
  85 .I x
  86 is a NaN, a NaN is returned.
  87
  88 If
  89 .I x
  90 is +0 (\-0), +0 (\-0) is returned.
  91
  92 If
  93 .I x
  94 is positive infinity (negative infinity),
  95 +1 (\-1) is returned.
  96
  97 If
  98 .I x
  99 is subnormal,
 100 a range error occurs,
 101 and the return value is 2*x/sqrt(pi).
 102 .SH ERRORS
 103 See
 104 .BR math_error (7)
 105 for information on how to determine whether an error has occurred
 106 when calling these functions.
 107 .PP
 108 The following errors can occur:
 109 .TP
 110 Range error: result underflow (\fIx\fP is subnormal)
 111 .\" .I errno
 112 .\" is set to
 113 .\" .BR ERANGE .
 114 An underflow floating-point exception
 115 .RB ( FE_UNDERFLOW )
 116 is raised.
 117 .PP
 118 These functions do not set
 119 .IR errno .
 120 .\" FIXME . Is it intentional that these functions do not set errno?
 121 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6785
 122 .SH CONFORMING TO
 123 C99, POSIX.1-2001.
 124 The variant returning
 125 .I double
 126 also conforms to
 127 SVr4, 4.3BSD.
 128 .SH SEE ALSO
 129 .BR cerf (3),
 130 .BR erfc (3),
 131 .BR exp (3)