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As this post will illustrate, I'm a total VBA noob. I've been trying to write an interative solver for a system of equations, using a 'do while...." loop. The program seems to disagree that my variable inputs are valid, I'm currently assigning variables from a spreadsheet using the 'range' function.
Currently the debugger flags the bolded line with Error 5 - Invalid Call or Argument
Any input very apprecaited, I'm stumped.
The Code
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Option Explicit
Sub Iterate_PEMU_Parameters()
'Iterative solver to solve equilibria equations; specifically designed for PEMU films
'Assign Variables
Dim Kp As Double, Ki As Double, Cs As Double 'Constants
Dim F As Double, P As Double, I As Double 'where X = Px, representing the polymers in different forms
Dim F0 As Double, P0 As Double, I0 As Double 'old values of above
Dim C As Double 'Concentration of Ions
Dim y As Double 'Activity Coefficient
Dim x As Double, z As Double 'Changes in Concentration
Dim h As Double, k As Double, o As Double 'Film Thickness, Swelling Constant, old thickness (h0)
Dim ConvergeFlag As Boolean 'Convergence Flag
Dim Counter As Double, OldCounter As Double 'Iteration Counter
'Retrieve Initial Inputs
Kp = Worksheets("Sheet1").Range("B1").Value
Ki = Worksheets("Sheet1").Range("B2").Value
Cs = Worksheets("Sheet1").Range("B3").Value
F = Worksheets("Sheet1").Range("B4").Value
P = Worksheets("Sheet1").Range("B5").Value
I = Worksheets("Sheet1").Range("B6").Value
ConvergeFlag = 0
Counter = 0
'Set h to 1
k = (F + I) / P
h = 1
o = 1
'Iterative Loop
Do While ConvergeFlag = 0
'Equations for one iteration
y = 10 ^ (-0.51 * Sqr(F + Cs))
x = (-(4 * y * F + P) - Sqr((4 * y * F + Kp) ^ 2 - 4 * (4 * y) * (y * (F ^ 2) - Kp * P))) / (2 * 4 * y)
If x < 0 Then
x = (-(4 * y * F + P) - Sqr((4 * y * F + Kp) ^ 2 - 4 * (4 * y) * (y * (F ^ 2) - Kp * P))) / (2 * 4 * y)
Else
End If
z = (-(-y * Cs - y * F - Ki) - Sqr((-y * Cs - y * F - Ki) ^ 2 - 4 * (y) * (y * F * Cs - Ki * I))) / (2 * y)
If z < 0 Then
z = (-(-y * Cs - y * F - Ki) + Sqr((-y * Cs - y * F - Ki) ^ 2 - 4 * (y) * (y * F * Cs - Ki * I))) / (2 * y)
Else
End If
'Store New Values
F = F + 2 * x - z
P = P - x
I = I + z
'Calculate new Thickness
o = h
h = k * (2 * P) / (F + I)
'Correct for Concentrations
F0 = F
F = F0 * (h / o)
P0 = P
P = P0 * (h / o)
I0 = I
I = I0 * (h / o)
'Convergence Test
If x < 0.0001 And y < 0.0001 Then ConvergeFlag = 1
'Count Iterations
OldCounter = Counter
Counter = OldCounter + 1
If Counter > 100000 Then
MsgBox "Iteration limit reached. Guess better next time, noob!", 48
ConvergeFlag = 1
End If
Loop
'Report Answers
Worksheets("sheet1").Range("D1").Value = ("Results")
Worksheets("sheet1").Range("D2").Value = ("Pf")
Worksheets("sheet1").Range("D3").Value = ("Pp")
Worksheets("sheet1").Range("D4").Value = ("Pi")
Worksheets("sheet1").Range("D5").Value = ("h")
Worksheets("sheet1").Range("D6").Value = ("y")
Worksheets("sheet1").Range("D7").Value = ("Ks")
Worksheets("sheet1").Range("D8").Value = ("Iterations")
Worksheets("sheet1").Range("E2").Value = F
Worksheets("sheet1").Range("E3").Value = P
Worksheets("sheet1").Range("E4").Value = I
Worksheets("sheet1").Range("E5").Value = h
Worksheets("sheet1").Range("E6").Value = y
Worksheets("sheet1").Range("E7").Value = k
Worksheets("sheet1").Range("E8").Value = Counter
End Sub
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