Butcher and Chartier in [1, pp. 274–276] first introduced the doubly
companion matrices, after that Butcher and Wright [2] and Wright [3] used of
doubly companion matrices as a tool to analyze numerical methods and some gen-
eral linear methods property. In this paper, we prove that any doubly companion
matrix, and the sum of two doubly companion matrices are nonderogatory, and
obtain the explicit form of its minimal polynomials. Moreover, we construct some
examples which show that those product of two doubly companion matrices may
not be a nonderogatory matrix. As in [4], we gives some condition for which the
product of (doubly) companion matrices is a nonderogatory matrix. In addition
we assert that the product of two unreduced Hessenberg is not nonderogatory.