Re: strange behaviour for VCR

On Monday 14 April 2008, [email protected] wrote:
> I was writing a frontend for ngspice-xspice above netbeans in
> java for educational purpose (I'm teacher) and I was
> interested by a more interactive simulator. So I decided to
> test gnucap. I am satisfied with it but also concerned by
> strange behaviour above xp and Linux. I'm using gnucap-0.35

Welcome ..   I prefer to start students in the interactive text 
mode.  Most GUI's make it harder.

> I don't know if it is a bug or if I misunderstand something.
> So please, show clemency, I spend a lot of time to delimit
> this strange behaviour.

It's a bug in the limiting algorithm.

> If I try without the line "V30 30 0 1000.0", I obtain strange
> result : the voltage of the node 11 is 32.77E+12.
> If I uncomment this line, I have good result for the VCR.
> (329.34 V which is the theoretical result). This Voltage
> source would be useless !
>
> Perhaps it's a stupid error but I don't understand...

The voltage source (1000 volts) tells the simulator's limiting 
algorithm that 1000 volts is reasonable.  Without it, it thinks 
such high voltages in a 15 volt transistor circuit are signs of 
something wrong, and it tries to fix them.

For now, turn this part of limiting off:
.options vmax=1e99 vmin=-1e99

The default values of vmax and vmin are starting points.  They 
automatically adjust, but didn't in this case.





>
> Best regards
>
> Jacques Le Coupanec
>
>
>
>
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