d4r22.frm

来自「常用数值算法集哈」· FRM 代码 · 共 106 行

VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "Form1"
   ClientHeight    =   2685
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   3945
   LinkTopic       =   "Form1"
   ScaleHeight     =   2685
   ScaleWidth      =   3945
   StartUpPosition =   3  'Windows Default
   Begin VB.CommandButton Command1 
      Caption         =   "Command1"
      Height          =   375
      Left            =   2280
      TabIndex        =   0
      Top             =   2040
      Width           =   1335
   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 D4R22
    'Driver for routine BESSK0
    Dim ACTUAL(5), X(5)
    ACTUAL(1) = 1.752704
    ACTUAL(2) = 0.4210244
    ACTUAL(3) = 0.3185082
    ACTUAL(4) = 0.1138939
    ACTUAL(5) = 0.003691098
    X(1) = 0.2
    X(2) = 1#
    X(3) = 1.2
    X(4) = 2#
    X(5) = 5#
    Print
    Print "    X        Actual        BESSK0(X)"
    For I = 1 To 5
        Print Tab(4); Format$(X(I), "#0.##");
        Print Tab(10); Format$(ACTUAL(I), ".0000000E+00");
        Print Tab(26); Format$(BESSK0(X(I)), ".0000000E+00")
    Next I
End Sub
Function BESSK0(X)
    P1 = -0.57721566
    P2 = 0.4227842
    P3 = 0.23069756
    P4 = 0.0348859
    P5 = 0.00262698
    P6 = 0.0001075
    P7 = 0.0000074
    Q1 = 1.25331414
    Q2 = -0.07832358
    Q3 = 0.02189568
    Q4 = -0.01062446
    Q5 = 0.00587872
    Q6 = -0.0025154
    Q7 = 0.00053208
    If X <= 2# Then
        Y# = X * X / 4#
        BBB = Y * (P5 + Y * (P6 + Y * P7))
        AAA# = P1 + Y * (P2 + Y * (P3 + Y * (P4 + BBB)))
        BESSK0 = (-Log(X / 2#) * BESSI0(X)) + AAA#
    Else
        Y# = (2# / X)
        BBB = Y * (Q5 + Y * (Q6 + Y * Q7))
        AAA# = Q1 + Y * (Q2 + Y * (Q3 + Y * (Q4 + BBB)))
        BESSK0 = (Exp(-X) / Sqr(X)) * AAA#
    End If
End Function
   Function BESSI0(X)
      P1 = 1#
      P2 = 3.5156229
      P3 = 3.0899424
      P4 = 1.2067492
      P5 = 0.2659732
      P6 = 0.0360768
      P7 = 0.0045813
      Q1 = 0.39894228
      Q2 = 0.01328592
      Q3 = 0.00225319
      Q4 = -0.00157565
      Q5 = 0.00916281
      Q6 = -0.02057706
      Q7 = 0.02635537
      Q8 = -0.01647633
      Q9 = 0.00392377
      If Abs(X) < 3.75 Then
          Y = (X / 3.75) ^ 2
          AAA = Y * (P5 + Y * (P6 + Y * P7))
          BESSI0 = P1 + Y * (P2 + Y * (P3 + Y * (P4 + AAA)))
      Else
          AX = Abs(X)
          Y = 3.75 / AX
          AAA = Exp(AX) / Sqr(AX)
          BBB = Q4 + Y * (Q5 + Y * (Q6 + Y * (Q7 + Y * (Q8 + Y * Q9))))
          BESSI0 = AAA * (Q1 + Y * (Q2 + Y * (Q3 + Y * BBB)))
      End If
   End Function