regress/roff/if/close-rules.in

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  28 .\"     from: @(#)erf.3 6.4 (Berkeley) 4/20/91
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  31 .Dd April 20, 1991
  32 .Dt ERF 3
  33 .Os
  34 .Sh NAME
  35 .Nm erf ,
  36 .Nm erff ,
  37 .Nm erfc ,
  38 .Nm erfcf
  39 .Nd error function operators
  40 .Sh SYNOPSIS
  41 .In math.h
  42 .Ft double
  43 .Fn erf "double x"
  44 .Ft float
  45 .Fn erff "float x"
  46 .Ft double
  47 .Fn erfc "double x"
  48 .Ft float
  49 .Fn erfcf "float x"
  50 .Sh DESCRIPTION
  51 These functions calculate the error function of
  52 .Fa x .
  53 .Pp
  54 The
  55 .Fn erf
  56 and the
  57 .Fn erff
  58 functions calculate the error function of x; where
  59 .Bd -ragged -offset indent
  60 .if n \{\
  61 erf(x) = 2/sqrt(pi)\(**\|integral from 0 to x of exp(\-t\(**t) dt.
  62 1234 \} asdf
  63 1234 \} asdf
  64 .if t \{\
  65 erf\|(x) :=
  66 (2/\(sr\(*p)\|\(is\d\s8\z0\s10\u\u\s8x\s10\d\|exp(\-t\u\s82\s10\d)\|dt.
  67 4321 \} fdsa
  68 4321 \} fdsa
  69 .Ed
  70 .Pp
  71 The
  72 .Fn erfc
  73 and the
  74 .Fn erfcf
  75 functions calculate the complementary error function of
  76 .Fa x ;
  77 that is
  78 .Fn erfc
  79 subtracts the result of the error function
  80 .Fn erf x
  81 from 1.0.
  82 This is useful, since for large
  83 .Fa x
  84 places disappear.
  85 .Sh SEE ALSO
  86 .Xr math 3
  87 .Sh HISTORY
  88 The
  89 .Fn erf
  90 and
  91 .Fn erfc
  92 functions appeared in
  93 .Bx 4.3 .