Re: @above in analyses other than tran and dc sweep

The existence of multiple dc operating points is generally
swept under the rug.  The fact is, the results of the
simulation of such a circuit can depend on the initial
guess in Newton's method, or whether one is even using
Newton or another solution method.

So, you can either decide that @above has no meaning, because
you expect your simulator to evaluate a dc sweep by randomly
picking an order to evaluate the points, or you can be
pragmatic about it and decide that every spice-like
simulator I know of uses the previous sweep point as a
starting point for the current one, and therefore @above
could give you useful information.

I suppose there's really no reason to assume that a simulator
uses Newton's method to solve the circuit, in which case the
fact that the ddx() operator requests the symbolic derivative
is making some unwarranted assumption about how the simulator
works; how dare we assume it needs a Jacobian?

-Geoffrey


Ian Wilson wrote:
> Suppose we run two simulations at values a,b,c for some swept variable, x.
> 
> Surely the results for the simulation with x=b should be the same 
> regardless of
> whether x had the value a or c in some previous simulation?
> 
> I would expect all DC simulations of a circuit with hysteresis to 
> produce the
> same result (for the same parameter values), since there is no concept 
> of a previous
> state (unless you allow the simulator to start from the operating point 
> calculated in some
> other step).
> 
> --ian


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