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Re: [Help-gnucap] Time step control

From: a r
Subject: Re: [Help-gnucap] Time step control
Date: Tue, 19 Feb 2008 13:24:19 +0000

On Feb 19, 2008 6:19 AM, al davis <address@hidden> wrote:
> If there are no storage elements, there is no truncation error,
> but there is still "activity", and step control is still
> needed.

I agree it doesn't work well in every case but for most circuits (i.e.
those with storage elements) truncation error is a reasonable
estimation of the circuit activity. You are using it in trap method
after all and it works quite well (except for ringing which is an
inherent "feature" of trap method).

> For the future, there are plans to add node-voltage-change based
> time step control.

That would be great, assuming it'd work reliably without manual
intervention. However, I see it as a great supplement for the LTE
based time step control, not a replacement for it.

> Truncation error is only loosely related to circuit activity,
> usually too little, too late.  That is why it is still possible
> to see trap ringing sometimes.

What other simulators are using (spectre, hspice etc.)? Whatever it is
it works well enough for them - I've never had to fiddle with their
time step control options except for some tricky circuits.

Again, I am quite satisfied with the results of trap method. There are
some numerical artifacts but I can live with them. I would only wish
euler method to perform similarly well - currently it is only usable
for fixed time step transient simulations.

BTW, is it possible to enable LTE check in euler method in the source
code? If it's not very difficult I'd like to test it a bit.



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