不完全 函数定义为：
其互补形式
当 时，可以利用 的级数展开求不完全 函数：
当，可以用如下连分式求解不完全 函数：
求解 的级数形式：
Public Function gammaser(ByVal a As Double, ByVal x As Double) As Double
Dim EPS, sum, del, ap, lng As Double
EPS = getGDelta()
Dim ITMAX, n As Long
ITMAX = 1000
lng = lnGamma(a)
If x < 0# Then
gammaser = -1
Exit Function
End If
If x = 0# Then
gammaser = 0#
Exit Function
End If
If a <= getGDelta() Then
gammaser = -1
Exit Function
End If
ap = a
del = 1# / a
sum = del
For n = 0 To ITMAX - 1
ap = ap + 1
del = del * x / ap
sum = sum + del
If (Abs(del) < Abs(sum) * EPS) Then
gammaser = sum * Exp(-x + a * Log(x) - lng)
Exit Function
End If
Next
gammaser = 1 / EPS
End Function
求解 的连分式形式：
Public Function gammacf(ByVal a As Double, ByVal x As Double) As Double
Dim ITMAX, i As Long
Dim an, b, C, d, del, h, EPS, FPMIN, lng As Double
ITMAX = 1000
EPS = getGDelta()
FPMIN = 0.000000000001
lng = lnGamma(a)
b = x + 1# - a
C = 1# / FPMIN
d = 1# / b
h = d
For i = 1 To ITMAX
an = -i * (i - a)
b = b + 2#
d = an * d + b
If (Abs(d) < FPMIN) Then d = FPMIN
C = b + an / C
If (Abs(C) < FPMIN) Then C = FPMIN
d = 1# / d
del = d * C
h = h * del
If (Abs(del - 1#) <= EPS) Then
Exit For
End If
Next
If i > ITMAX Then
gammacf = 1# / FPMIN
Else
gammacf = Exp(-x + a * Log(x) - lng) * h
End If
End Function
求解：
Public Function gammap(ByVal a As Double, ByVal x As Double) As Double
If (x < 0# Or a <= getGDelta()) Then
Err.Raise vbObjectError + 513, , "参数错误！ "
End If
If (x < a + 1#) Then
gammap = gammaser(a, x)
Else
gammap = 1# - gammacf(a, x)
End If
End Function
getGDelta：获取用户在ExcelSTat中配置的精度。
ExcelStat下载： Excel加载宏ExcelStat.xla
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