Re: [ng-spice-devel] convergence
On Thu, 26 Apr 2001, Steve Hamm wrote:
> Yup. This was Quarles' "improvement" over spice2 -- he removed
> Nagel's old linearization check and just checks delta-solution, in
> ni/niconv.c, except he changes the absolute tolerance depending on
> whether its a KCL equation or a voltage source/inductor/etc.
> constraint equation.
Now I know why it seemed different than I remember. Didn't early
versions of Spice3 (3c??) have that check and it disappeared later?
Anyway, last time I spent any time on that, Spice2 was all that was
available.
> Sounds like ACS doesn't directly check KCL either. True?
True.
When the device level checks are adequate, does the KCL check really
do anything?
Also, unless I am missing something obvious, it is an expensive
operation. It means another pass with full model evaluations. Doing
it from the matrix will only show round-off errors in solving the
matrix, which are rarely a problem. Even if the matrix is
ill-conditioned, the dominant error is usually in building the
matrix, not solving it.
Actually, KCL almost always passes, even if it is not converged. The
iterative process generates a linearized equivalent circuit at an
operating point. If the linearization is wrong, a KCL check for the
incorrect circuit will still pass.
Partial thread listing:
- Re: [ng-spice-devel] convergence, (continued)