VBA root finding trough bisection - vba

Question

My vba code keeps returning a value of 0 when I know the roots of my function are not 0.
It's pretty simple code but I can't seem to debug it. Any idea where this error might be coming from??
Option Explicit
Public Function Bisect(ByVal xlow As Double, ByVal xhigh As Double) As Double
Dim i As Integer
Dim xmid As Double
xmid = (xlow + xhigh) / 2
For i = 1 To 100
If f(xlow) * f(xmid) < 0 Then
xhigh = xmid
xmid = (xlow + xhigh) / 2
Else
xlow = xmid
xmid = (xlow + xhigh) / 2
End If
Next i
Bisect = xmid
End Function
Function f(ByVal x As Double, Optional ByRef inputArray As Range) As Variant
Dim ca0 As Double
Dim v0 As Double
Dim k As Double
Dim e As Double
Dim ac As Double
Dim L As Double
inputArray(2, 2) = ca0
inputArray(3, 2) = v0
inputArray(4, 2) = k
inputArray(5, 2) = e
inputArray(6, 2) = ac
inputArray(7, 2) = L
f(x) = (v0 / (k * ca0 * ac)) * ((2 * e * (1 + e) * Log(1 - x)) + (e ^ 2 * x) + (((1 + e) ^ 2 * x) / (1 - x))) - L
End Function

Answer 1

' i Think you want to take those constant values from cells presentin the sheet
Function f(ByVal x As Double) As Variant
Dim inputArray As Range
Dim ca0 As Double
Dim v0 As Double
Dim k As Double
Dim e As Double
Dim ac As Double
Dim L As Double
' i Think you want to take values from cells in the sheet
ca0 = ActiveSheet.Cells(2, 2).Value
v0 = ActiveSheet.Cells(3, 2).Value
k = ActiveSheet.Cells(4, 2).Value
e = ActiveSheet.Cells(5, 2).Value
ac = ActiveSheet.Cells(6, 2).Value
L = ActiveSheet.Cells(7, 2).Value

Answer 2

Could it be that you try to assign the inputarray with empty variables?
In my mind it should be:
ca0 = inputArray(2, 2)
v0 = inputArray(3, 2)
And so on.
I'm guessing
f(x) = (v0 / (k * ca0 * ac)) * ((2 * e * (1 + e) * Log(1 - x)) + (e ^ 2 * x) + (((1 + e) ^ 2 * x) / (1 - x))) - L
Should be
f = (v0 / (k * ca0 * ac)) * ((2 * e * (1 + e) * Log(1 - x)) + (e ^ 2 * x) + (((1 + e) ^ 2 * x) / (1 - x))) - L