computing Rollet factor K with shunt resistor at collector

Does anyone know how to compute the admittance matrix of a transistor in shunt with a resistor at it's collector. Basically I need to compute new K value after shunt resistor stabilization of transistor. The only information I have is [s] for transistor at operation frequency and also the shunt resistance required. I need to be able to get new S matrix in order to get new K value so I can work out MAG. Please help

See the followings.

http://en.wikipedia.org/wiki/Scattering_parameters
http://www.rfcafe.com/references/electrical/s-h-y-z.htm

[S] --> [Y]={y11, y12 ; y21, y22}
[Ynew]={y11, y12 ; y21, y22+Gshunt}
[Ynew] --> [Snew]

see here to see how calculate

http://uwaverf.altervista.org/index....d=48&Itemid=53