泊松分布m.bas

<VB数理统计实用算法>书中的算法源程序

Attribute VB_Name = "modMethod"
'泊松分布
Option Explicit
'计算符合泊松分布事件的概率
'n：试验次数
'p：一次试验中事件A出现的概率
'x：n次试验中事件A出现的次数
'Poi：事件A出现x次的概率
Public Sub Poisson(n As Integer, p As Single, x As Integer, Poi As Double)
    Dim L As Double, E As Double, X1 As Double, I As Integer
    X1 = 0
    For I = 1 To x
        X1 = X1 + Log(I)
    Next I
    L = n * p
    E = x * Log(L) - L - X1
    Poi = Exp(E)
End Sub

'计算泊松分布函数
'n：试验次数
'p：一次试验中事件A出现的概率
'x：事件A出现的次数
'A(1,0 To x)：事件概率
'A(2,0 To x)：下侧概率，即分布函数
'A(3,0 To x)：上侧概率
Public Sub APoisson(n As Integer, p As Single, x As Integer, A() As Double)
    Dim y As Integer, B As Double
    B = 0
    For y = 0 To x
        Poisson n, p, y, A(1, y)
        B = B + A(1, y)
        If B > 1 Then B = 1
        A(2, y) = B
        A(3, y) = 1 - B
    Next y
End Sub