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Re: [Help-gnucap] Bizarre behaviour -- possibly a bug.

From: al davis
Subject: Re: [Help-gnucap] Bizarre behaviour -- possibly a bug.
Date: Sun, 26 May 2013 04:05:16 -0400
User-agent: KMail/1.13.7 (Linux/3.2.0-4-amd64; KDE/4.8.4; x86_64; ; )

On Saturday 25 May 2013, Orestes Mas wrote:
> All elements are in series, so clearly I(Vg)=-I(L1)
> But instead, the first output value of I(Vg) is -900kA, and
> should be zero.  Current through the inductor is OK.
> This does not happen if "UIC" is removed from TRAN command.
> Why? Are voltage  independent sources using initial
> conditions internally?

"It's Not A Bug, It's A Feature!"

Spice avoids the problem by not printing anything for time=0 
when you do UIC.  Gnucap plainly shows that UIC is screwed up, 
as it implements bug-for-bug compatibility.

UIC does not give reasonable results, by design.  It just makes 
all voltages zero, jam sets capacitor and inductors initial 
conditions without regard to consequences.  Think of it as 
jamming a bunch of ideal voltage and current sources into the 

The purpose of UIC is so you can do a transient analysis on a 
circuit that does not have a stable DC operating point.

In this case, with option short=10u, it is shorting the 9 volt 
voltage source, and correctly reporting a current of 900 

> Ah, I nearly forgot it: I'm using Gnucap 2009.12.07 RCS
> 26.136. Not tested  with stable release.

You might want to upgrade ..  the latest snapshot is  2013.04.23 
RCS 26.138.

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