Re: [ng-spice-devel] convergence


To ng-spice-devel@ieee.ing.uniroma1.it
From Steve Hamm <Steve.Hamm@motorola.com>
Date Mon, 30 Apr 2001 09:51:11 -0500 (CDT)
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---"Al" == Al Davis <aldavis@ieee.org> writes:

Al> Actually, both are inconsistent.

Al> With form 1, x is solved using the latest state variables, which
Al> may not match what you get using the latest x.  With form 2, the
Al> state variables are solved using the latest x, which may not match
Al> what you get when you apply the state variables you have.

I'm not sure how you get "form 2" being inconsistent.

In "form 2", when the iteration quits, F and J are evaluated at x_n
and the accepted solution is x_n, so everything is consistent.

Al> But, at convergence it doesn't matter.  The error is bounded.

I expect that this is often true, but given the sloppy checking in
spice, I expect that this difference could account for some timestep
problems, since, for instance, capacitor charge won't correspond to
the voltage across the branch.

--Steve

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