ngspice/README.optran

Adding transient simulation top generate the operating point of a circuit

The operating point of a circuit has to be established before a transient, ac, 
or noise simulation may be started.

The procedure, as found in cktop.c is as follows:
1) Iterate the matrix with the starting values
If this fails:
2) Start gmin stepping
If this fails:
3) start source stepping

If this again fails, bail out.

In tghis branch a fourth method is added:
4) Start a transient simulation for a specific amount of time.
   Keep all data local. Keep the matrix values as an
   operating point for the simualtion following.
If this fails, finally stop.

The time for transient is determined a priori. If a transient
simulation follows, choose 100 time the TSTEP value. If an ac
or noise simulation follows, take the inverted starting
frequency divided by 10 as the optran simulation time.

A method to stop the op transient simulation, when all nodes
have become stable, might be desirable, but has not yet been implemented.

Step 1 may be skipped by
option noopiter

Step 2 may be skipped by
option gminsteps=0

Step 3 may be skipped by 
option srcsteps=0