'invalid control variable reference' error

[JenkinsMeechelle]

Hi all,
I am trying to copy an example from a textbook so that i can edit it for my own use and i have typed out the Macro they apparently used. i Have checked a few time and can't see the error but i keep getting a 'invalid control variable reference' error and can't get any further. I would appreciate any help on fixing this issue! The code is copied directly from VBA below.

DefDbl A-H, K-L, P-Z
DefLng I-J, M-O
Sub Fig8_1()
Dim aold(256), anew(256), Vz(256)
Dim A(256), B(256), C(256), D(256)


ain = 1
Da = 0.000000005
L = 2
R = 0.01
U = 0.01
k = 0.005
Itotal = 2


For jj = 1 To 7 'this outer loop varies Itotal to check convergence
    Itotal = 2 * Itotal
    If Itotal = 4 Then Jtotal = 2
    If Itotal = 8 Then Jtotal = 4
    If Itotal > 8 Then Jtotal = 8 * Jtotal
    dr = R / Itotal
    dz = L / Jtotal


'Set constants in Eq 8.26
    A(0) = 4 * Da / dr ^ 2 * dr / 2 / U
    B(0) = -4 * Da / dr ^ 2 * dz / 2 / U
    D(0) = -k * dz / 2 / U
    aold(0) = 1


'Set constants in Eq 8.25
   For i = 1 To Itotal - 1
    Vz(i) = 2 * U * (1 - (i * dr) ^ 2 / R ^ 2)
    A(i) = Da * (1 / (2 * dr ^ 2 * i) + 1 / dr ^ 2) * dz / Vz(i)
    B(i) = Da * (-2 / dr ^ 2) * dz / Vz(i)
    C(i) = Da * (-1 / (2 * dr ^ 2 * i) + 1 / dr ^ 2) * dz / Vz(i)
    D(i) = -k * dz / Vz(i)
    aold(i) = 1
   Next


'Set the initial conditions
   For i = 0 To Itotal
    aold(i) = ain
   Next


'March down the tube
   For j = 1 To Jtotal
    anew(0) = A(0) * aold(1) + (1 + B(0)) * aold(0) + D(0) * aold(0)
   
'This is the sideways shuffle
   For i = 1 To Itotal - 1
    x = A(i) * aold(i + 1) + (1 + B(i)) * aold(i)
    anew(i) = x + C(i) * aold(i - 1) + D(i) * aold(i)
   Next j
    Next i


'Apply the wall boundary condition, Eq 8.27
   anew(Itotal) = 4 * anew(Itotal - 1) / 3 - anew(Itotal - 2) / 3
   
'March a step forward
   For i = 0 To Itotal
    aold(i) = anew(i)
   Next i
'Calculate the mixing cup average
    F = 0
    Q = 0
   For i = 1 To Itotal - 1
    F = F + 2 * dr * i * Vz(i) * anew(i)
    Q = Q + 2 * dr * i * Vz(i)
   Next i
   y = F / Q
'Output results for this mesh size
    Range("A" & CStr(jj)).Select
    ActiveCell.FormulaR1C1 = Itotal
    Range("B" & CStr(jj)).Select
    ActiveCell.FormulaR1C1 = Jtotal
    Range("C" & CStr(jj)).Select
    ActiveCell.FormulaR1C1 = y
    
    Next jj
        
End Sub

 

[Norie]

Swap these around.

Next j
Next i

 

[JenkinsMeechelle]

I should have mentioned that the error specifically refers to the 'Next J' term in the 'This is the sideways shuffle section

 

[Norie]

That's where the code I'm referring to comes from.

It should be this.

Next i
Next j

 

[JenkinsMeechelle]

yes! Norie
i love you a little bit