Using Matrices In Formulas, Using Letters As Input In Userforms

I have a matrix with default probabilities. I have this matrix in my worksheet. The user will give the number of periods to be calculated with and it will result in a new matrix with default periods over time of choice.

Private Sub UserForm_Click()
Dim numberof_text_Change As Single
Dim initial_text_Change As Single

Range("U36:AC44").Select
Selection.FormulaArray = "=matrixpower(R[-10]C:R[-2]C[8],numberof_text.value)"
End Sub

matrixpower is a function that works perfectly well. It takes one matrix as an argument and the number of periods to use. It then simply computes the chosen number of powers of my matrix. I have a userform that has an inputbox called numberof_text which specifies the number of periods that the user wishes to use in calculating the chance of default. Hence I would like to use this variable as an argument in the formulaarray. This doesn't seem to work! I only get "#VALUE!" in every cell. If I replace "numberof_text.value" in the matrixpower function with a number it works fine. What to do?

What the function needs to do is take an argument which is the matrix I have on my spreadsheet. Take the number of times to take powers of the matrix and print it on a pre-specified place on the worksheet. If I cannot use variables with FormulaArrays, then is there another good way of choosing the matrix to use with "powermatrix"?