d4r21.frm

来自「常用数值算法集哈」· FRM 代码 · 共 79 行

VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "Form1"
   ClientHeight    =   2820
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   3990
   LinkTopic       =   "Form1"
   ScaleHeight     =   2820
   ScaleWidth      =   3990
   StartUpPosition =   3  'Windows Default
   Begin VB.CommandButton Command1 
      Caption         =   "Command1"
      Height          =   375
      Left            =   2160
      TabIndex        =   0
      Top             =   2160
      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 D4R21
    'Driver for routine BESSI0
    Dim ACTUAL(5), X(5)
    ACTUAL(1) = 1.010025
    ACTUAL(2) = 1.266066
    ACTUAL(3) = 1.393726
    ACTUAL(4) = 2.279585
    ACTUAL(5) = 27.23987
    X(1) = 0.2
    X(2) = 1#
    X(3) = 1.2
    X(4) = 2#
    X(5) = 5#
    Print
    Print "    X         Actual       BESSI0(X)"
    For I = 1 To 5
        Print Tab(4); Format$(X(I), "#0.##");
        Print Tab(12); Format$(ACTUAL(I), ".0000000E+00");
        Print Tab(26); Format$(BESSI0(X(I)), ".0000000E+00")
    Next I
End Sub
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