initial

Initial condition response of state-space model

Syntax

```initial(sys,x0) initial(sys,x0,Tfinal) initial(sys,x0,t) initial(sys1,sys2,...,sysN,x0) initial(sys1,sys2,...,sysN,x0,Tfinal) initial(sys1,sys2,...,sysN,x0,t) [y,t,x] = initial(sys,x0) [y,t,x] = initial(sys,x0,Tfinal) [y,t,x] = initial(sys,x0,t) ```

Description

`initial(sys,x0)` calculates the unforced response of a state-space (`ss`) model `sys` with an initial condition on the states specified by the vector `x0`:

`$\begin{array}{cc}\stackrel{˙}{x}=Ax,& x\left(0\right)={x}_{0}\\ y=Cx& \end{array}$`

This function is applicable to either continuous- or discrete-time models. When invoked without output arguments, `initial` plots the initial condition response on the screen.

`initial(sys,x0,Tfinal)` simulates the 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```), `initial` interprets `Tfinal` as the number of sampling periods to simulate.

`initial(sys,x0,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 `0:Ts:Tf`, where `Ts` is the sample time. For continuous-time models, `t` should be of the form `0:dt:Tf`, where `dt` becomes the sample time of a discrete approximation to the continuous system (see `impulse`).

To plot the initial condition responses of several LTI models on a single figure, use

`initial(sys1,sys2,...,sysN,x0)`

`initial(sys1,sys2,...,sysN,x0,Tfinal)`

`initial(sys1,sys2,...,sysN,x0,t)`

(see `impulse` for details).

When invoked with output arguments,

`[y,t,x] = initial(sys,x0)`

`[y,t,x] = initial(sys,x0,Tfinal)`

`[y,t,x] = initial(sys,x0,t)`

return the output response `y`, the time vector `t` used for simulation, and the state trajectories `x`. No plot is drawn on the screen. The array `y` has as many rows as time samples (length of `t`) and as many columns as outputs. Similarly, `x` has `length(t)` rows and as many columns as states.

Examples

collapse all

Plot the response of the following state-space model:

`$\begin{array}{rcl}\left[\begin{array}{l}{\underset{}{\overset{˙}{x}}}_{1}\\ {\underset{}{\overset{˙}{x}}}_{2}\end{array}\right]& =& \left[\begin{array}{cc}-0.5572& -0.7814\\ 0.7814& 0\end{array}\right]\left[\begin{array}{l}{x}_{1}\\ {x}_{2}\end{array}\right]\\ y& =& \left[\begin{array}{cc}1.9691& 6.4493\end{array}\right]\left[\begin{array}{l}{x}_{1}\\ {x}_{2}\end{array}\right].\end{array}$`

Take the following initial condition:

`$x\left(0\right)=\left[\begin{array}{l}1\\ 0\end{array}\right].$`

```a = [-0.5572, -0.7814; 0.7814, 0]; c = [1.9691 6.4493]; x0 = [1 ; 0]; sys = ss(a,[],c,[]); initial(sys,x0)```

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.

Version History

Introduced before R2006a