rowregul — removing poles and zeros at infinity
[Stmp,Ws]=rowregul(Sl,alfa,beta)
    computes a postfilter Ws such that Stmp=Ws*Sl 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 a assumed to be a right invertible linear system (syslin list)
    in state-space representation with possibly a polynomial D matrix.
This function is the dual of colregul (see function code).