VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "Form1"
   ClientHeight    =   5550
   ClientLeft      =   2460
   ClientTop       =   945
   ClientWidth     =   4575
   LinkTopic       =   "Form1"
   ScaleHeight     =   5550
   ScaleWidth      =   4575
   Begin VB.CommandButton Command1 
      Caption         =   "Command1"
      Height          =   375
      Left            =   2520
      TabIndex        =   0
      Top             =   4800
      Width           =   1455
   End
End
Attribute VB_Name = "Form1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Private Sub Command1_Click()
    'PROGRAM D4R10
    'Driver for routine ERF
    Open "D:\VB常用數值算法集\DATA\FNCVAL.DAT" For Input As #1
    Do
      Line Input #1, Text$
    Loop While Text$ <> "Error Function"
    Line Input #1, NVAL$
    NVAL = Val(NVAL$)
    Print Text$
    Print
    Print "    X        Actual       ERF(X)"
    For I = 1 To NVAL
        Line Input #1, DUM$
        X = Val(Mid(DUM$, 1, 6))
        Value = Val(Mid(DUM$, 7))
        Print Tab(4); Format$(X, "#0.0#");
        Print Tab(12); Format$(Value, "0.0000000");
        Print Tab(25); Format$(ERF(X), "0.0000000")
    Next I
    Close #1
End Sub
Function ERF(X)
    If X < 0# Then
        ERF = -GAMMP(0.5, X ^ 2)
    Else
        ERF = GAMMP(0.5, X ^ 2)
    End If
End Function
Function ERFC(X)
    If X < 0# Then
        ERFC = 1# + GAMMP(0.5, X ^ 2)
    Else
        ERFC = GAMMQ(0.5, X ^ 2)
    End If
End Function
Function ERFCC(X)
    Z = Abs(X)
    T = 1# / (1# + 0.5 * Z)
    DDD = -0.82215223 + T * 0.17087277
    AAA = T * (-1.13520398 + T * (1.48851587 + T * DDD))
    BBB = T * (-0.18628806 + T * (0.27886807 + AAA))
    CCC = T * (0.37409196 + T * (0.09678418 + BBB))
    ERFCC = T * Exp(-Z * Z - 1.26551223 + T * (1.00002368 + CCC))
    If X < 0# Then ERFCC = 2# - ERFCC
End Function
   Function GAMMP(A, X)
      If X < 0# Or A <= 0# Then
         Print "PAUSE"
         Exit Function
      End If
      If X < A + 1# Then
          Call GSER(GAMSER, A, X, GLN)
          GAMMP = GAMSER
      Else
          Call GCF(GAMMCF, A, X, GLN)
          GAMMP = 1# - GAMMCF
      End If
   End Function
  Function GAMMQ(A, X)
      If X < 0# Or A <= 0# Then
         Print "PAUSE"
         Exit Function
      End If
      If X < A + 1# Then
          Call GSER(GAMSER, A, X, GLN)
          GAMMQ = 1# - GAMSER
      Else
          Call GCF(GAMMCF, A, X, GLN)
          GAMMQ = GAMMCF
      End If
   End Function
   Sub GSER(GAMSER, A, X, GLN)
      ITMAX = 100
      EPS = 0.0000003
      GLN = GAMMLN(A)
      If X <= 0# Then
          If X < 0# Then
             Print " PAUSE"
             Exit Sub
          End If
          GAMSER = 0#
          Exit Sub
      End If
      AP = A
      Sum = 1# / A
      DEL = Sum
      For N = 1 To ITMAX
          AP = AP + 1#
          DEL = DEL * X / AP
          Sum = Sum + DEL
          If Abs(DEL) < Abs(Sum) * EPS Then GoTo 1
      Next N
      Print "A too large, ITMAX too small"
1     GAMSER = Sum * Exp(-X + A * Log(X) - GLN)
   End Sub
   Sub GCF(GAMMCF, A, X, GLN)
      ITMAX = 100
      EPS = 0.0000003
      GLN = GAMMLN(A)
      GOLD = 0#
      A0 = 1#
      A1 = X
      B0 = 0#
      B1 = 1#
      FAC = 1#
      For N = 1 To ITMAX
          AN = N

          ANA = AN - A
          A0 = (A1 + A0 * ANA) * FAC
          B0 = (B1 + B0 * ANA) * FAC
          ANF = AN * FAC
          A1 = X * A0 + ANF * A1
          B1 = X * B0 + ANF * B1
          If A1 <> 0# Then
              FAC = 1# / A1
              G = B1 * FAC
              If Abs((G - GOLD) / G) < EPS Then GoTo 1
              GOLD = G
          End If
      Next N
      Print "A too large, ITMAX too small"
1     GAMMCF = Exp(-X + A * Log(X) - GLN) * G
   End Sub
   Function GAMMLN(XX)
      Dim COF(6)
      COF(1) = 76.18009173
      COF(2) = -86.50532033
      COF(3) = 24.01409822
      COF(4) = -1.231739516
      COF(5) = 0.00120858003
      COF(6) = -0.00000536382
      STP = 2.50662827465
      HALF = 0.5
      ONE = 1#
      FPF = 5.5
      X = XX - ONE
      TMP = X + FPF
      TMP = (X + HALF) * Log(TMP) - TMP
      SER = ONE
      For J = 1 To 6
          X = X + ONE
          SER = SER + COF(J) / X
    Next J
      GAMMLN = TMP + Log(STP * SER)
   End Function