Both dc and transient solutions are obtained by an iterative process which is terminated when both of the following conditions hold:
Although the algorithm used in NGSPICE has been found to be very reliable, in some cases it fails to converge to a solution. When this failure occurs, the program terminates the job.
Failure to converge in dc analysis is usually due to an error in
specifying circuit connections, element values, or model parameter
values. Regenerative switching circuits or circuits with positive
feedback probably will not converge in the dc analysis unless the
OFF
option is used for some of the devices in the feedback path,
or the .NODESET
control line is used to force the circuit to
converge to the desired state.