Guide to QucsStudio: Circuit Simulator with C++/Octave Support

(1) Transient analysis is unreliable. Jacobian error. Jacobian error. JACOBIAN ERROR. Fixing this involves magic thought patterns (is there something in this circuit that might be unstable? maybe throwing resistors everywhere will help? Or changing the minimum timestep?) and luck. I have spent more time dealing with this than any other thing in this software; often it's easier to give up and build the circuit IRL.

The software gives you NO hints or help as to what is causing these sim divergences or how to fix it. Brick wall. I exploit a bug to get the graphs to re-render using only the half-calculated results, so I can _try_ to see the circuit behaviour just before the issue, but often this doesn't work.

EDIT: Sorry the article does touch on this in the conclusion:

> Obviously, QucsStudio also has its limitations. It is sometimes frustrating to find that a simulation stops converging when a parameter is slightly changed. In general, using QucsStudio requires a deeper knowledge than other tools, typically paid tools, where the convergence of simulations is more refined. This can lead to unexpected delays in the design process.

Frustrating indeed >:(

(2) Interface uses an old version of Qt, which my distro doesn't provide the libs for. This means I can't compile or run Qucs any more. Instead I run the Windows .exe using wine (note: crashes if you have any themes/visual styles setup in winecfg, make sure to go back to the classic windows theme).

Are either of these things improved in QucsStudio?

I didn't realize that QUCS-S did EM simulation (section 3.1.6.2 in this article) and I'm curious what the features/limitations are. The killer feature in a tool like this for signal integrity applications would be support for IBIS or IBIS-AMI models for time donation simulation... There's a great FOSS simulator for AMI but it's not integrated with a schematic environment.

Considering how slowly EDA/simulation tools move combined with their insane cost, it's an area that's certainly ready for a FOSS tool to move in the way software tools have gone.

If I recall correctly, he more or less rage quit after people were using his work to design some pretty advanced RF stuff for sale, but weren't able to pay him to develop some more advanced simulation capabilities.

He's posted a few cryptic comments saying that he's built support for full EM transverse mode simulation but won't release it publicly.