实现Excel和VB的IRR功能

=IRR(现金流1, 现金流2, 现金流3, ...)

Function IRR(cashFlows As Variant, guess As Double) As Double
    Dim rate As Double
    Dim maxIterations As Integer
    Dim tolerance As Double
    Dim iteration As Integer
    Dim npv As Double
    Dim fValue As Double
    Dim fValueOld As Double
    Dim rateStep As Double
    
    maxIterations = 100
    tolerance = 0.0001
    rateStep = 0.05
    
    guess = guess / 100
    rate = guess
    
    For iteration = 1 To maxIterations
        npv = 0
        fValue = 0
        For i = 0 To UBound(cashFlows)
            If i = 0 Then
                npv = npv + cashFlows(i)
            Else
                npv = npv + cashFlows(i) / (1 + rate) ^ i
            End If
        Next i
        fValue = npv
        If Abs(fValue)< tolerance Then
            IRR = rate * 100
            Exit Function
        End If
        If iteration = 1 Then
            fValueOld = fValue
        End If
        If fValue * fValueOld < 0 Then
            rate = rate - rateStep
        Else
            rate = rate + rateStep
        End If
        rateStep = rateStep / 2
        fValueOld = fValue
    Next iteration
End Function