Main Content

Compute and test residuals

`resid(`

computes
the 1-step-ahead prediction errors (residuals) for an identified model, `Data`

,`sys`

)`sys`

,
and plots residual-input dynamics as one of the following, depending
on the data in`Data`

:

For time-domain data,

`resid`

plots the autocorrelation of the residuals and the cross-correlation of the residuals with the input signals. The correlations are generated for lags -25 to 25. To specify a different maximum lag value, use`residOptions`

. The 99% confidence region marking statistically insignificant correlations displays as a shaded region around the X-axis.For frequency-domain data,

`resid`

plots a bode plot of the frequency response from the input signals to the residuals. The 99% confidence region marking statistically insignificant response is shown as a region around the X-axis.

To change display options, right-click the plot to access the context menu. For more details about the menu, see Tips.

`resid(`

computes
and plots the residual of multiple identified models `Data`

,sys1,...,sysn)`sys1`

,...,`sysn`

.

Right-clicking the plot opens the context menu, where you can access the following options:

**Systems**— Select systems to view the residual correlation or response plots. By default, all systems are plotted.**Show Confidence Region**— View the 99% confidence region marking statistically insignificant correlations. Applicable only for the correlation plots.**Data Experiment**— For multi-experiment data only. Toggle between data from different experiments.**Characteristics**— View data characteristics. Not applicable for correlation plots.**Peak Response**— View peak response of the data.**Confidence Region**— View the 99% confidence region marking statistically insignificant response.

**Show**— Applicable only for frequency-response plots.**Magnitude**— View magnitude of frequency response.**Phase**— View phase of frequency response.

**I/O Grouping**— For datasets containing more than one input or output channel. Select grouping of input and output channels on the plot. Not applicable for correlation plots.**None**— Plot input-output channels in their own separate axes.**All**— Group all input channels together and all output channels together.

**I/O Selector**— For datasets containing more than one input or output channel. Select a subset of the input and output channels to plot. By default, all output channels are plotted.**Grid**— Add grids to the plot.**Normalize**— Normalize the y-scale of all data in the plot. Not applicable for frequency-response data.**Full View**— Return to full view. By default, the plot is scaled to full view.**Initial Condition**— Specify handling of initial conditions.Specify as one of the following:

**Estimate**— Treat the initial conditions as estimation parameters.**Zero**— Set all initial conditions to zero.**Absorb delays and estimate**— Absorb nonzero delays into the model coefficients and treat the initial conditions as estimation parameters. Use this option for discrete-time models only.

**Properties**— Open the Property Editor dialog box to customize plot attributes.

[1] Ljung, L. *System Identification: Theory for
the User*. Upper Saddle River, NJ: Prentice-Hall PTR, 1999,
Section 16.6.