Issue in using VBA for Finite Difference Method - vba

Question

The question to be done
I have tried this out.
I have created few functions. I am confused in the remaining ones.
I have made the first function and stored the values of upper, lower and main matrix in my spreadsheet.
Function createFEMatrixDirichlet(a, C, Nx, h, dt)
Dim k As Integer
'Main
For k = 0 To Nx - 1
Cells(k + 2, 2).Value = 1 - dt * (((2 * a) / (h * h)) + x)
Next k
'Lower
For k = 0 To Nx - 2
Cells(k + 2, 1).Value = dt * (a / (h * h))
Next k
'Upper
For k = 0 To Nx - 3
Cells(k + 2, 3).Value = dt * (a / (h * h))
Next k
End Function
Nodes are generated similar way.
Function nodeGeneration(xa, xb, Nx, column)
Dim k As Integer
'Find h
h = (xb - xa) / Nx
'Generate Node
For k = 0 To Nx
Cells(k + 2, column).Value = xa + k * h
Next k
End Function
Initial condition are applied:
Function applyInitialCondition(Nx, column)
Dim k As Integer
For k = 0 To Nx
Cells(k + 2, column).Value = ((Cells(k + 2, 4)) + 2) / 2
Next k
End Function
Now to multiply I am a bit confused. My implementation is that I am trying to make the entire matrix and then multiply. However, there is no luck. Some or the other error pops up.
Also, I have no idea on how to implement the FETimeStep and then create a new subroutine to run the entire code.
Any leads?
Sample Input