Re: Proposal for two additional environment parameter functions

Arpad -
$abstime works OK in a transient analysis, because the full model is evaluated
at each timepoint.

Spice's ac analysis is a different sort of animal: the operating point is
computed, and then *the circuit is linearized about that op-pt*.  Generally,
this means that the model is evaluated during the op-pt and all the derivatives
are stored off.  Then, for each point in the ac analysis, the derivatives are
used to compute J = G + j w C, where G=conductances and C=capacitances
(derivatives of contributions involving ddt()); G and C are *not* re-computed
at the new frequency, because Spice assumes that they only depend on the
v-vector (the operating point).

I agree with David (from Tiburon) about the hazards of $freq expressions
for models that are supposed to work in transient, HB, etc.

-Geoffrey


Muranyi, Arpad wrote:
> Geoffrey,
> 
> I don't understand the reason for why the IF statement
> wouldn't get evaluated during the AC sweep.   Could
> you please explain that to me?
> 
> If we had this in the language, I would expect it to
> work the same as $abstime.  Doesn't $abstime=0 in the
> operating point analysis and greater than zero
> thereafter?  If I remember correctly, I was able to
> use if($abstime ...) before.  Why couldn't $freq do
> the same?
> 
> Thanks,
> 
> Arpad

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