The dc analysis portion of ngspice determines the dc operating point of the circuit with inductors shorted and capacitors opened. The dc analysis options are specified on the .DC, .TF, and .OP control lines.

There is assumed to be no time dependence on any of the sources within the system description. The simulator algorithm subdivides the circuit into those portions that require the analog simulator algorithm and such that require the event-driven algorithm. Each subsystem block is then iterated to solution, with the interfaces between analog nodes and event-driven nodes iterated for consistency across the entire system.

Once stable values are obtained for all nodes in the system, the analysis halts and the results may be displayed or printed out as you request them.

A dc analysis is automatically performed prior to a transient analysis to determine the transient initial conditions, and prior to an ac small-signal analysis to determine the linearized, small-signal models for nonlinear devices. If requested, the dc small-signal value of a transfer function (ratio of output variable to input source), input resistance, and output resistance is also computed as a part of the dc solution. The dc analysis can also be used to generate dc transfer curves: a specified independent voltage, current source, resistor or temperature is stepped over a user-specified range and the dc output variables are stored for each sequential source value.