Interesting paper in IEEE Transactions on CAD

I have not well understood the details of this post but I am very interested 
in the topic from a user perspective.

I think that you (and the cited paper) are dealing with the possibility of 
perform a fast resimulation of the circuit after having made a change of a 
circuit part (trough a partial update of the LU decomposition).
I am interested in this capability because I would like to implement a 
design/optimization strategy for microwave components which is based on a
Electromagnetic software I am developing. This software will produce an 
equivalent circuit that is composed of many subcircuits describing the 
different parts (subvolumes) of the component.
The optimization process typically changes only a  few of the subcircuits but 
the variations are not smooth because of the casualty of  some algorithms 
(like remeshing) and because the equivalent circuits are not unique. So I can 
not make use of the sensitivity versus a small variation of the discrete 
parameters and I am wondering if it is possible to apply the partial update 
of the LU decomposition after having replaced a subcircuit with a new one 
(which can also have a different number of elements). I have seen that gnucap 
offers some commands which allow to change the value of a discrete component 
but is it possible to replace an entire subcircuit ?

Thanks for your attention

Walter Steffè