How to Plot Impulse and Step Response Using the App

To create a transient analysis plot in the System Identification app, select the Transient resp check box in the Model Views area. For general information about creating and working with plots, see Working with Plots.

To include or exclude a model on the plot, click the corresponding model icon in the System Identification app. Active models display a thick line inside the Model Board icon.

The following table summarizes the Transient Response plot settings.

Transient Response Plot Settings

ActionCommand
Display step response for linear or nonlinear model.

Select Options > Step response.

Display impulse response for linear model.

Select Options > Impulse response.

    Note:   Not available for nonlinear models.

Display the confidence interval.

    Note:   Only available for linear models.

  • To display the dashed lines on either side of the nominal model curve, select Options > Show confidence intervals. Select this option again to hide the confidence intervals.

  • To change the confidence value, select Options > Set % confidence level, and choose a value from the list.

  • To enter your own confidence level, select Options > Set confidence level > Other. Enter the value as a probability (between 0 and 1) or as the number of standard deviations of a Gaussian distribution.

Change time span over which the impulse or step response is calculated. For a scalar time span T, the resulting response is plotted from -T/4 to T.

    Note:   To change the time span of models you estimated using correlation analysis models, select Estimate > Correlation models and reestimate the model using a new time span.

  • Select Options > Time span (time units), and choose a new time span in units of time you specified for the model.

  • To enter your own time span, select Options > Time span (time units) > Other, and enter the total response duration.

  • To use the time span based on model dynamics, type [] or default.

    The default time span is computed based on the model dynamics and might be different for different models. For nonlinear models, the default time span is 10.

Toggle between line plot or stem plot.

    Tip   Use a stem plot for displaying impulse response.

Select Style > Line plot or Style > Stem plot.

(Multiple-output system only)
Select an input-output pair to view the noise spectrum corresponding to those channels.

Select the output by name in the Channel menu.

If the plotted models include a noise model, you can display the transient response properties associated with each output channel. The name of the channel has the format e@OutputName, where OutputName is the name of the output channel corresponding to the noise model.

(Step response for nonlinear models only)
Set level of the input step.

    Note:   For multiple-input models, the input-step level applies only to the input channel you selected to display in the plot.

Select Options > Step Size, and then chose from two options:

  • 0–>1 sets the lower level to 0 and the upper level to 1.

  • Other opens the Step Level dialog box, where you enter the values for the lower and upper level values.

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