VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "Form1"
   ClientHeight    =   3195
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   4680
   LinkTopic       =   "Form1"
   ScaleHeight     =   3195
   ScaleWidth      =   4680
   StartUpPosition =   3  'Windows Default
   Begin VB.CommandButton Command1 
      Caption         =   "Command1"
      Height          =   375
      Left            =   3120
      TabIndex        =   0
      Top             =   2640
      Width           =   1215
   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 D3R2
    'Driver for routine QTRAP
    PIO2 = 1.5707963
    A = 0#
    B = PIO2
    Print
    Print Tab(5); "Integral of FUNC computed with QTRAP"
    Print
    Print Tab(5); "Actual value of integral is:";
    Print Tab(34); Format$((FINT(B) - FINT(A)), "0.####00")
    Print
    Call QTRAP(A, B, S)
    Print Tab(5); "Result from routine QTRAP is:";
    Print Tab(35); Format$(S, "0.####00")
End Sub
Function FUNC(X)
    FUNC = (X ^ 2) * (X ^ 2 - 2#) * Sin(X)
End Function
Function FINT(X)
    'Integral of FUNC
    AAA = 4# * X * (X ^ 2 - 7#) * Sin(X)
    FINT = AAA - (X ^ 4 - 14# * X ^ 2 + 28#) * Cos(X)
End Function
Sub QTRAP(A, B, S)
    EPS = 0.000001
    JMAX = 20
    OLDS = -1E+30
    For J = 1 To JMAX
        Call TRAPZD(A, B, S, J)
        If Abs(S - OLDS) < EPS * Abs(OLDS) Then Exit Sub
        OLDS = S
    Next J
    Print "Too many steps."
End Sub
    Sub TRAPZD(A, B, S, N)
       If N = 1 Then
           S = 0.5 * (B - A) * (FUNC(A) + FUNC(B))
           IT = 1
       Else
           IT = 2 ^ (N - 2)
           TNM = IT
           DEL = (B - A) / TNM
           X = A + 0.5 * DEL
           Sum = 0#
           For J = 1 To IT
               Sum = Sum + FUNC(X)
               X = X + DEL
           Next J
           S = 0.5 * (S + (B - A) * Sum / TNM)
       End If
    End Sub