removing poles and zeros at infinity
[Stmp,Ws]=colregul(Sl,alfa,beta)
:Sl,Stmp syslin lists : :alfa,beta reals (new pole and zero positions) :
computes a prefilter Ws such that Stmp=Sl*Ws is proper and with full rank D matrix.
Poles at infinity of Sl are moved to alfa;
Zeros at infinity of Sl are moved to beta;
Sl is assumed to be a left invertible linear system ( syslin list) in state-space representation with possibly a polynomial D matrix.