stepplot
Plot step response and return plot handle
Syntax
h = stepplot(sys)
stepplot(sys,Tfinal)
stepplot(sys,t)
stepplot(sys1,sys2,...,sysN)
stepplot(sys1,sys2,...,sysN,Tfinal)
stepplot(sys1,sys2,...,sysN,t)
stepplot(AX,...)
stepplot(..., plotoptions)
stepplot(..., dataoptions)
Description
h = stepplot(sys) plots the step response
of the dynamic
system model sys. It also returns
the plot handle h. You can use this handle to customize
the plot with the getoptions and setoptions commands.
Type
help timeoptions
for a list of available plot options.
For multiinput models, independent step commands are applied to each input channel. The time range and number of points are chosen automatically.
stepplot(sys,Tfinal) simulates the step
response from t = 0 to the final time t
= Tfinal. Express Tfinal in the system
time units, specified in the TimeUnit property
of sys. For discrete-time systems with unspecified
sample time (Ts = -1), stepplot interprets Tfinal as
the number of sampling intervals to simulate.
stepplot(sys,t) uses the user-supplied
time vector t for simulation. Express t in
the system time units, specified in the TimeUnit property
of sys. For discrete-time models, t should
be of the form Ti:Ts:Tf, where Ts is
the sample time. For continuous-time models, t should
be of the form Ti:dt:Tf, where dt becomes
the sample time of a discrete approximation to the continuous system
(see step). The stepplot command
always applies the step input at t=0, regardless
of Ti.
To plot the step responses of multiple models sys1,sys2,...
on a single plot, use:
stepplot(sys1,sys2,...,sysN)
stepplot(sys1,sys2,...,sysN,Tfinal)
stepplot(sys1,sys2,...,sysN,t)
You can also specify a color, line style, and marker for each system, as in
stepplot(sys1,'r',sys2,'y--',sys3,'gx')
stepplot(AX,...) plots into the axes with
handle AX.
stepplot(..., plotoptions) customizes the plot appearance using the
options set, plotoptions. Use timeoptions to create the options set.
stepplot(..., dataoptions) specifies options
such as the step amplitude and input offset using the options set, dataoptions.
Use stepDataOptions to
create the options set.
Examples
Display Normalized Response on Step Plot
Generate a step response plot for two dynamic systems.
sys1 = rss(3); sys2 = rss(3); h = stepplot(sys1,sys2);
Each step response settles at a different steady-state value. Use the plot handle to normalize the plotted response.
setoptions(h,'Normalize','on')
Now, the responses settle at the same value expressed in arbitrary units.
Plot Step Responses of Identified Models with Confidence Region
Compare the step response of a parametric identified model to a nonparametric (empirical) model, and view their 3-σ confidence regions. (Identified models require System Identification Toolbox™ software.)
Identify a parametric and a nonparametric model from sample data.
load iddata1 z1 sys1 = ssest(z1,4); sys2 = impulseest(z1);
Plot the step responses of both identified models. Use the plot handle to display the 3-σ confidence regions.
t = -1:0.1:5; h = stepplot(sys1,sys2,t); showConfidence(h,3) legend('parametric','nonparametric')
The nonparametric model sys2 shows higher uncertainty.
Plot Step Response of Nonlinear Identified Model
Load data for estimating a nonlinear Hammerstein-Wiener model.
load(fullfile(matlabroot,'toolbox','ident','iddemos','data','twotankdata')); z = iddata(y,u,0.2,'Name','Two tank system');
z is an iddata object that stores the input-output estimation data.
Estimate a Hammerstein-Wiener Model of order [1 5 3] using the estimation data. Specify the input nonlinearity as piecewise linear and output nonlinearity as one-dimensional polynomial.
sys = nlhw(z,[1 5 3],pwlinear,poly1d);
Create an option set to specify input offset and step amplitude level.
opt = stepDataOptions('InputOffset',2,'StepAmplitude',0.5);
Plot the step response until 60 seconds using the specified options.
stepplot(sys,60,opt);
Tips
You can change the properties of your plot, for example the units. For information on the ways to change properties of your plots, see Ways to Customize Plots.
See Also
getoptions | setoptions | step