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.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.
Temperature (TEMP) and resistance sweeps have been introduced
in NGSPICE, they were not available in the original code of Spice3f5.