Use Initial Conditions problem in Spice 3f5.


To <ng-spice-devel@ieee.ing.uniroma1.it>
From "Jon Engelbert" <jon@beigebag.com>
Date Mon, 23 Apr 2001 19:17:44 -0400
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In-Reply-To <Pine.LNX.3.96.1010419210725.28011A-100000@ieee.ing.uniroma1.it >
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On my copy of Spice 3f5, I've noticed that when the transient condition
"uic" is specified there is quirky behavior.
With UIC specified...
sources start at zero, regardless of their dc value or their initial
transient value.
Also, I think that capacitors with no initial condition specified start with
0 volts across them.

In NIITER.C, you find the following code within the Niiter function.

    if( (ckt->CKTmode & MODETRANOP) && (ckt->CKTmode & MODEUIC)){
                temp = ckt->CKTrhsOld;
                ckt->CKTrhsOld = ckt->CKTrhs;
                ckt->CKTrhs = temp;
                error = CKTload(ckt);
                if(error) {
                        return(error);
                }
                return(OK);
    }

This code is processed when UIC is specified, and a lot of other code is
skipped over.  I don't understand the transient routine well enough to fix
it, and it may have been fixed in ng-spice already but I don't know because
I haven't got it running yet.

At any rate, this is usually only a cosmetic problem affecting the first
data point only, however, with switches starting in their hysteresis region,
for example, the first point can be significant to the rest of the transient
run.

Jon Engelbert
President, Beige Bag Software
279 E. Liberty, Ann Arbor, MI 48105
jon@beigebag.com

-----Original Message-----
From: p.nenzi@ieee.org [mailto:pnenzi@ieee.ing.uniroma1.it]
Sent: Thursday, April 19, 2001 3:08 PM
To: ng-spice-devel@ieee.ing.uniroma1.it
Subject: [ng-spice-devel] Wow. look.

http://lc.cray.com/spice3/

Bye,
Paolo


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