"transient" command


Performs a nonlinear time domain (transient) analysis.


transient start stop stepsize {options ...}
transient stepsize stop start {options ...} 


The probes to look at must have been previously selected by the print or plot command.

Three parameters are normally needed for a Transient analysis: start time, stop time and step size, in this order. The SPICE order (step size, stop, start) is also acceptable. An optional fourth parameter is the maximum internal time step.

If all of these are omitted, the simulation will continue from where the most recent one left off, with the same step size, unless the circuit topology has been changed. It will run for the same length of time as the previous run.

Do not use a step size too large as this will result in errors in the results. If you suspect that the results are not accurate, try a larger argument to skip. This will force a smaller internal step size. If the results are close to the same, they can be trusted. If not, try a still larger skip argument until they appear to match close enough.

The most obvious error of this type is aliasing. You must select sample frequency at least twice the highest signal frequency that exists anywhere in the circuit. This frequency can be very high, when you use the default step function as input. The signal generator does not have any filtering.


Sweep control

dtmax time The maximum internal time step. (Default = stepsize/skip)
dtmin time The minimum internal time step. (Default = option dtmin) Time cannot be resolved closer than this.
dtratio number The minimum internal time step, as a ratio. (Default = option dtratio) This is the maximum number of internal time steps for every requested step.
skip count Force at least count internal transient time steps for each one displayed. If the output is a table or ASCII plot, the extra steps are hidden, unless the trace option specifies to print them.

Input / Output

> file Send results of analysis to file.
» file Append results to file.
noplot Suppress plotting.
plot Graphic output, when plotting is normally off.
quiet Suppress console output.
trace off No extended trace information.
trace warnings Show extended warnings.
trace alltime Show all accepted internal time steps.
trace rejected Show all internal time steps including rejected steps.
trace iterations Show every iteration.
trace verbose Show extended diagnostics.


dtemp degrees Temperature offset, degrees C. Add this number to the temperature from the options command.
temperature degrees Temperature, degrees C.
cold Zero initial conditions. Cold start from power-up.
uic Use initial conditions. Do not do an initial DC analysis. Instead, use the values specified with the IC = options on the various elements, and set everything else to zero. In most cases, UIC is not recommended. Improper use of UIC causes more problems than it solves. It is the way it is for Spice compatibility.


transient 0 100u 10n

Start at time 0, stop after 100 micro-seconds. Simulate using 10 nanosecond steps.


No parameters mean to continue from the last run. In this case it means to step from 100 us to 200 us in 10 ns steps. (The same step size and run length, but offset to start where the last one stopped.

transient skip 10

Do 10 extra steps internally for every step that would be done otherwise. In this case it means to internally step at 1 nanosecond. If the output is in tabular form, the extra steps are hidden.

transient 0

Start over at time = 0. Keep the same step size and run length.

transient >arun

Save the results of this run in the file “arun”.

gnucap/manual/commands/transient.txt · Last modified: 2015/12/11 15:39 (external edit)
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