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similar to a diagonal matrix, so that there exists a non-singular 
matrix P such that (®): 
(5.21) 
DB =PHP 
where H is diagonal and has for diagonal elements the latent 
roots of DB. Let: 
(5.22) 
(5-23) 
(5.24) 
Then every such term can bè Writctai € 
(5.25) (DB) DVI(o:- 
PH 
DO. 
30 
We know that every diagonal element of the diagonal 
matrix A is less than unity in absolute value (indeed, we are 
assuming that some of the diagonal elements are zero). More 
over, if we are prepared to maintain the stability assumption 
on DB which was slipped in some time ago, every diagonal 
element of the diagonal matrix H will also be less than unity 
in absolute value. It follows that every element of every term 
in the expansion of W(1) other than the first is composed of 
a sum of terms each of which involves at least the product of 
(*) The assumption involved is, of course. very weak and is made for 
pase of exposition 
6 | 
Fisher - pag. 37