RE: [ng-spice-devel] Use Initial Conditions problem in Spice 3f5.
Alan,
You're right.
This is from the SPICE manual.
"UIC is an optional keyword which indicates that the user does not want
SPICE to solve for the quiescent operating point before beginning the
transient analysis. If this keyword is specified, SPICE uses the values
specified using IC = ... on the various elements as the initial transient
condition and proceeds with the analysis. ..."
I'd recommend changing it so that voltage sources are set at their initial
transient value in addition to using .IC settings.
I haven't looked at the code, but does anyone know if the state reported at
time zero is even consistent when UIC is used? I'll try to set up a test
case tomorrow.
Jon Engelbert
President, Beige Bag Software
279 E. Liberty, Ann Arbor, MI 48105
jon@beigebag.com
-----Original Message-----
From: Gillespie, Alan [mailto:Alan.Gillespie@analog.com]
Sent: Thursday, April 26, 2001 5:43 AM
To: 'ng-spice-devel@ieee.ing.uniroma1.it'
Subject: RE: [ng-spice-devel] Use Initial Conditions problem in Spice 3f5.
> 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.
As far as I understand it, that's what UIC is supposed to
do. There's no initial attempt at a DC solution, and everything
starts either at 0, or at the IC defined on the device line.
With the .IC card, spice will actually try to find initial
convergance with all the nodes held as they're defined on the
.IC line. I can't remember if Berkeley Spice uses the IC=
parameter on the devices in this mode. Some Spices do, others
don't.
The whole area of .IC, IC= and UIC has been interpreted
different ways by different Spices. Maybe we should state
a definition.
Cheers,
Alan
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