You can only use Matrix.Rows.Count if Matrix is a range object (or in your
case a variant containing a range object).

But XtoN does not return a Range, it returns a Variant containing a
2-dimensional array of numbers, so the outer call has Matrix as a variant
and Matrix.Rows.Count fails.

You either need to test what type of data Matrix contains, or (probably
better) just assign it to a variant:
something like this (not tested)

Function XtoN(Matrix as variant, N) as variant
Dim i as long
Dim M as variant

M=Matrix ''' converts range to variant containing an array

Fraction = Abs(N) - Int(Abs(N))
If Fraction < 0 Then
If ubound(M,1)< ubound(m,2) Or Fraction < 0 Then
MsgBox "X must be a Square Matrix" & vbNewLine & "N must be an
Integer = 1"
Exit Function
End If
end if


B = Matrix
For i = 1 To N - 1
B = WorksheetFunction.MMult(Matrix, B)
Next i
XtoN = B

End Function


Charles
__________________________________________________
Outlines for my Sessions at the Australia Excel Users Group
http://www.decisionmodels.com/OZEUC.htm

"LesHurley" wrote in message
...
About a week ago I posted a question about using VBA functions in
formulas.
Here
it is again with a much simpler function. XtoN raises a square matrix to
an
integer power. The code is as follows. Notice that the third line is
active
while the fourth is commented. As it stands here the call
=xton(xton(M,2),2)
works ok but an essential test is missing. If I comment the third line
and
make the fourth line active, the same call makes the function crash. Can
anyone say why, and how can I make the same test without crashing?

Function XtoN(Matrix, N)
Fraction = Abs(N) - Int(Abs(N))
'(Line 3)
If Fraction < 0 Then
'(Line 4)
'If Matrix.Rows.Count < Matrix.Columns.Count Or Fraction < 0 Then
MsgBox "X must be a Square Matrix" & vbNewLine & "N must be an
Integer = 1"
Exit Function
End If

Dim i As Integer

B = Matrix
For i = 1 To N - 1
B = WorksheetFunction.MMult(Matrix, B)
Next i
XtoN = B
End Function


'Thanks for your help