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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  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  2008-07-29 "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 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE; or
  55 .I cc\ -std=c99
  56 .br
  57 .BR erff (),
  58 .BR erfl (),
  59 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600|| _ISOC99_SOURCE; or
  60 .I cc\ -std=c99
  61 .ad b
  62 .SH DESCRIPTION
  63 The
  64 .BR erf ()
  65 function returns the error function of \fIx\fP, defined
  66 as
  67 .TP
  68     erf(x) = 2/sqrt(pi)* integral from 0 to x of exp(\-t*t) dt
  69 .SH RETURN VALUE
  70 On success, these functions return the error function of
  71 .IR x ,
  72 a value in the range [\-1,1].
  73
  74 If
  75 .I x
  76 is a NaN, a NaN is returned.
  77
  78 If
  79 .I x
  80 is +0 (\-0), +0 (\-0) is returned.
  81
  82 If
  83 .I x
  84 is positive infinity (negative infinity),
  85 +1 (\-1) is returned.
  86
  87 If
  88 .I x
  89 is subnormal,
  90 a "range error" occurs,
  91 and the return value is 2*x/sqrt(pi).
  92 .SH ERRORS
  93 See
  94 .BR math_error (7)
  95 for information on how to determine whether an error has occurred
  96 when calling these functions.
  97 .PP
  98 The following errors can occur:
  99 .TP
 100 Range error: result underflow (\fIx\fP is subnormal)
 101 .\" .I errno
 102 .\" is set to
 103 .\" .BR ERANGE .
 104 An underflow floating-point exception
 105 .RB ( FE_UNDERFLOW )
 106 is raised.
 107 .PP
 108 These functions do not set
 109 .IR errno .
 110 .\" FIXME . Is it intentional that these functions do not set errno?
 111 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6785
 112 .SH "CONFORMING TO"
 113 C99, POSIX.1-2001.
 114 The variant returning
 115 .I double
 116 also conforms to
 117 SVr4, 4.3BSD.
 118 .SH "SEE ALSO"
 119 .BR cerf (3),
 120 .BR erfc (3),
 121 .BR exp (3)