Add Array Formulas To Mutiple Ranges

I would like to set up VBA codes to generate a variable number of transition matrices. I would like to know how I can define dynamic ranges instead of coding each and every range. In the codes below, I have to define each range one by one instead of using a loop.

Sub TransitionMatrix()
Dim P1 As Range
Set P1 = Cells(2, 2).Resize(3, 3)
Dim P2 As Range
Set P2 = P1.Offset(5, 0).Resize(3, 3)
P2.Cells(0, 1) = "P2"
For i = 1 To 3
For j = 1 To 3
P2.FormulaArray = "=MMULT(" & P1.Address & "," & P1.Address & ")"
P2.BorderAround Weight:=xlMedium
Next j
Next i
Dim P3 As Range
Set P3 = P2.Offset(5, 0).Resize(3, 3)........................