Re: gEDA-user: Multiple pages

[al davis <ad252@xxxxxxxxxxxxxxxx>]

On Wednesday 18 August 2010, Oliver King-Smith wrote:
> I am under the probably incorrect impression that LtSpice is
> actually a better  than ngspice and gnucap.  What do you
> think the benefits are gnucap vs Ltspice?

Better for what?

You got that impression because somebody is promoting it and you 
believe the ads.

The biggest benefit of LTspice is that people like the user 
interface.  Also, it comes with a library of stuff that some 
users like.

The biggest drawback of the geda/gnucap combo is that the 
interface between gschem and gnucap works very badly, hence my 
request for help.  

Another issue with gnucap now is that there is a big difference 
between the stable branch and the development branch.  Some of 
the most important features are only in the development branch, 
which is not the one you get with most Linux distros.

For the benchmarks I have run, Gnucap outperforms LTspice and 
NGspice for medium to large circuits, sometimes by a huge 
amount.  I recall one where Gnucap completed a transient 
analysis in a few minutes, NGspice took about 8 hours, and I 
gave up waiting for LTspice, which had produced no output after 
running it overnight.  Also, Gnucap produces output along the 
way, so even with a slow run you get to see something soon, but 
either Spice doesn't show the user anything until it is all 
done.  This is not a random difference.  I fully understand the 
reasons for it.

Another benchmark, run a long time ago, comparing a predecessor 
of Gnucap to an expensive commercial simulator that specializes 
in power grid analysis, the predecessor of gnucap outperformed 
the commercial package for power grid analysis.

Gnucap is a lot more flexible that any spice.  It has plugins 
for lots of stuff, including models, measurements, simulation 
languages.  You can add new (lots of stuff) without recompiling 
or reinstalling.  It takes several simulation languages, 
including spice, spectre and Verilog.

Gnucap has more flexibility in how you run it, for example, you 
can do an AC analysis at an instant in time, such as a snapshot 
from a transient analysis.  Spice only lets you do AC at 
quiescent.  To see an example of where this matters, try doing 
an AC analysis of a class B amplifier.

Gnucap's step control works better.  One example of where this 
shows is in simulating oscillators.  Gnucap is accurate enough 
to make distortion measurements on a sine wave oscillator.  
Spice isn't.  Gnucap is accurate enough to properly simulate a 
negative resistance oscillator with a switch, and gives a 
correct waveform and correct oscillation frequency.  Either 
spice gives nonsense on this circuit.

Gnucap is not Spice.  (in the same sense that Gnu's not Unix, or 
that C++ is not Fortran)  Gnucap development is more focused on 
moving forward than bug-for-bug compatibility with legacy 
programs.

That's just a little.  But really, in free/open-source, or 
anywhere, you should expect tradeoffs.  One will be better in 
some ways, another better in other ways.  The question should 
not be which is better, but how do we make ours better.  That's 
both better than it is, and better than others.

And remember, things get better when you and we work to make 
them better, and worse when you see a perceived deficiency and 
run the other way, and worse when we deny the deficiencies and 
keep the status quo.

The Gnucap development team is working on features for advanced 
users, with the intent of eventually fully supporting Verilog-
AMS, through partnerships with some other GPL'd projects.   What 
seems to be missing is the partnership with schematic and 
layout.  It is in this area that help is most desperately 
needed.

Gnucap/gEDA can be made to be better that LTspice (and others 
too) in every way, if we choose to do so.  Let's do it.


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