[petsc-users] floating region help

[Jed Brown]

On Wed, Sep 21, 2011 at 05:51, Gong Ding <gdiso at ustc.edu> wrote:

> The background of this problem is the single event upset simulation of CMOS
> unit circuit, i.e. SRAM, latch, flip-flop.
> They all very big, ~ 1M mesh nodes. Direct method is too slow and memory
> consuming.
> Some stupid commercial code needs more than one week to simulate one
> particle event.
> People usually need 100-1000 events to determine the circuit behavior!
>
> Fortunately，the problem is in time domain. the transport equation of
> carrier has a d/dt term which helps stable.
> The most difficult part comes from metal connection. Just use above
> inverter, when both NMOS and PMOS are closed,
> the metal connection region has only displacement current from
> semiconductor region as eps*dE/dt, while metal region
> the current can be written as sigma*E. The current conservation here is the
> boundary condition at the metal-semiconductor interface.
> (Since E is \frac{\partical phi}{\partical n}, here phi is the independent
> variable)
>

How much does the time step help? Given the description, I'd expect not much
unless it's unreasonably short.


>
> Obviously, sigma >> eps/T, the governing equation of phi has a large jump
> parameter at the metal/semiconductor interface.
> The eigen value analysis confirmed that the number of samllest eigen value
> equals to the number of floating metal region.
> And the eigen vector is exactly the floating region.
>

Hmm, with a single low-energy mode, could you just start the Krylov method
with a nonzero initial guess and make the initial guess exactly this mode.
That would ensure that the Krylov space captures it exactly, and further
iterations should all come from picking up the rest of the modes.
Alternatively, you could formulate a modified system for which this mode was
removed analytically.

Just tossing out ideas here.
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