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