Assemble and extract matrices for non steady problem

Hello everybody,

I'm running Comsol directly from Matlab, and I wish to extract (among the others) the mass matrix for a fluid flow problem.

I do know how to extract matrices with the mphmatrix command, however this procedure (as described in the manuals of the Comsol 4.0a) doesn't work for transient problems. Did someone faced the same experience?

It seems that Comsol wants me to specify some "time" variable in order to run the command mphmatrix. To me this makes sense since (in general) Mass, Damping and even Stiffness matrices are not constant between two time steps.
But actually I don't know how to do that: I don't know how to ask Comsol "which linear system are you solving at time step 'K' ?".

I gave some tries, but even to specify 'Solnum' doesn't work.

Any idea?

Thanks,
Mattia