Re: [SI-LIST] : **error**: internal timestep too small

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From: Kim Helliwell ([email protected])
Date: Thu Jan 20 2000 - 10:15:51 PST

"Muranyi, Arpad" wrote:
> Kim and all,
> You can add a few more items to your bag:
> 1) Increase RELV, and/or RELI if it doesn't hurt your accuracy needs.

Well, that's what I meant by RELTOL. I was using Berkeley terminology,
not HSPICE terminology.

> 2) Use .IC to initialize nodes. Nodes that are (almost) floating
> can solve to about anything and setting them to something helps
> a great deal.

That helps with DC convergence issues, but I was giving my bag of
tricks for timestep problems. But of course you're right, and this
is an important early step for DC convergence.

> 3) I observed this with the U-element in HSPICE (anyone still using
> it?). If you connect more than two of them to the same node it
> will blow up (with kVolt differences on the two ends of the same
> element). However, a small resistor (yes, resistor) between the
> U-elements and the common joint will allow it to converge. Anyone
> knows why?

Hmmm, I don't know specifically. So you "float" the common joint
on a small resistor? Or is the resistor in series with and between
the two U's?

1 ohm resistors put 1s (or -1s) on the diagonal of the matrix, and
the more 1s on the diagonal, the better, in general. That's
why "cheater" resistors usually help in SPICE. But I doubt
that's the explanation here. At least, not the whole story.

> Arpad Muranyi
> Intel Corporation

Kim Helliwell
Senior CAE Engineer
Acuson Corporation
Phone: 650 694 5030  FAX: 650 943 7260

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