d4r26.frm

来自「常用数值算法集哈」· FRM 代码 · 共 108 行

VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "Form1"
   ClientHeight    =   2850
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   4080
   LinkTopic       =   "Form1"
   ScaleHeight     =   2850
   ScaleWidth      =   4080
   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 D4R26
    'Driver for routine BESSI
    Dim ACTUAL(5), X(5), N(5)
    ACTUAL(1) = 0.00501669
    ACTUAL(2) = 0.0221684
    ACTUAL(3) = 10.3312
    ACTUAL(4) = 0.00982568
    ACTUAL(5) = 0.00458
    N(1) = 2
    N(2) = 3
    N(3) = 3
    N(4) = 5
    N(5) = 10
    X(1) = 0.2
    X(2) = 1
    X(3) = 5
    X(4) = 2
    X(5) = 5
    Print
    Print "   N     X       Actual          BESSI(X)"
    For I = 1 To 5
        Print Tab(4); Format$(N(I), "#0.##");
        Print Tab(10); Format$(X(I), "#0.##");
        Print Tab(16); Format$(ACTUAL(I), ".000000E+00");
        Print Tab(32); Format$(BESSI(N(I), X(I)), ".000000E+00")
    Next I
End Sub
Function BESSI(N, X)
    IACC = 40
    BIGNO = 10000000000#
    BIGNI = 0.0000000001
    If N < 2 Then Print "bad argument N in BESSI"
    TOX = 2# / X
    BIP = 0#
    BI = 1#
    BESSI = 0#
    M = 2 * ((N + Int(Sqr(IACC * N))))
    For J = M To 1 Step -1
        BIM = BIP + J * TOX * BI
        BIP = BI
        BI = BIM
        If Abs(BI) > BIGNO Then
            BESSI = BESSI * BIGNI
            BI = BI * BIGNI
            BIP = BIP * BIGNI
        End If
        If J = N Then BESSI = BIP
    Next J
    BESSI = BESSI * BESSI0(X) / BI
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