 we choose matrix
 we choose matrix  in companion form, it is possible to give a very simple, explicit solution to unknown matrix
 in companion form, it is possible to give a very simple, explicit solution to unknown matrix  . It is furthermore shown that for almost all the matrices
 . It is furthermore shown that for almost all the matrices  , such that the pair (
 , such that the pair (  ) is reachable, matrix
 ) is reachable, matrix  is of full rank. All this allows us to establish efficient algorthims for designing reduced observers both for the estimate of state and for that of a given linear functional, even if the spectra of
 is of full rank. All this allows us to establish efficient algorthims for designing reduced observers both for the estimate of state and for that of a given linear functional, even if the spectra of  and
 and  are not disjointed.
 are not disjointed.