GAMMADIST(x,alpha,beta,cumulative)函数VB代码!!

发布网友发布时间：2022-06-15 03:20

共1个回答

热心网友时间：2023-10-22 20:54

简单的方法就是添加excel引用，然后：

dim xlApp as Excel.Application
Set xlApp = New Excel.Application
rt=xlApp.WorksheetFunction.GammaDist(x,alpha,beta,cumulative)

另外一种，从网上抄袭的哈，未验证：

Public Function GamCdf(x, a, b) '对应excel中GammaDist(x,a,b,true)函数
    If a <= 0 Or b <= 0 Then GammCdf = "NaN"
    GamCdf = GAMMAINC(x / b, a)
    p = IIf(p > 1, 1, p)
End Function

Public Function GAMMAINC(x, a)
Dim amax As Double
amax = 2 ^ 20
ascalar = 1
If a <= amax Then
   If a <> 0 And x <> 0 And x < a + 1 Then
        xk = x
        ak = a
        ap = ak
        Sum = 1 / ap
        del = Sum
        Dim i As Double
        For i = 1 To 10000
            ap = ap + 1
            del = xk * del / ap
            Sum = Sum + del
        Next
        GAMMAINC = Sum * Exp(-xk + ak * Log(xk) - GAMMALN(ak))
   ElseIf a <> 0 And x <> 0 And x >= a + 1 Then
       xk = x
       a0 = 1
       a1 = x
       b0 = 0
       b1 = a0
       ak = a
       fac = 1
       n = 1
       g = b1
       gold = b0
       For i = 1 To 10000
           gold = g
           ana = n - ak
           a0 = (a1 + a0 * ana) * fac
           b0 = (b1 + b0 * ana) * fac
           anf = n * fac
           a1 = xk * a0 + anf * a1
           b1 = xk * b0 + anf * b1
           fac = 1 / a1
           g = b1 * fac
           n = n + 1
       Next
       GAMMAINC = 1 - Exp(-xk + ak * Log(xk) - GAMMALN(ak)) * g
   End If
Else
   GAMMAINC="NaN"
End If
End Function

Public Function GAMMALN(XX)
Dim COF(6) As Double, stp As Double, half As Double, one As Double
Dim fpf As Double, x As Double, tmp As Double, ser As Double
Dim j As Integer
COF(1) = 76.18009173
COF(2) = -86.50532033
COF(3) = 24.01409822
COF(4) = -1.231739516
COF(5) = 0.00120858003
COF(6) = -0.00000536382
stp = 2.50662827465
half = 0.5
one = 1#
fpf = 5.5
x = XX - one
tmp = x + fpf
tmp = (x + half) * Log(tmp) - tmp
ser = one
For j = 1 To 6
   x = x + one
   ser = ser + COF(j) / x
Next j
GAMMALN = tmp + Log(stp * ser)
End Function