lsiminfo

Compute linear response characteristics

Syntax

S = lsiminfo(y,t,yfinal)
S = lsiminfo(y,t)
S = lsiminfo(...,'SettlingTimeThreshold',ST)


Description

S = lsiminfo(y,t,yfinal) takes the response data (t,y) and a steady-state value yfinal and returns a structure S containing the following performance indicators:

• SettlingTime — Settling time

• Min — Minimum value of Y

• MinTime — Time at which the minimum value is reached

• Max — Maximum value of Y

• MaxTime — Time at which the maximum value is reached

For SISO responses, t and y are vectors with the same length NS. For responses with NY outputs, you can specify y as an NS-by-NY array and yfinal as a NY-by-1 array. lsiminfo then returns an NY-by-1 structure array S of performance metrics for each output channel.

S = lsiminfo(y,t) uses the last sample value of y as steady-state value yfinal. s = lsiminfo(y) assumes t = 1:NS.

S = lsiminfo(...,'SettlingTimeThreshold',ST) lets you specify the threshold ST used in the settling time calculation. The response has settled when the error |y(t) - yfinal| becomes smaller than a fraction ST of its peak value. The default value is ST=0.02 (2%).

Examples

Compute Response Characteristics of a Transfer Function

Create the following continuous-time transfer function:

$$H(s)=\frac{s-1}{s^3+2s^2+3s+4}$$

sys = tf([1 -1],[1 2 3 4]);

Calculate the impulse response.

[y,t] = impulse(sys);

impulse returns the output response y and the time vector t used for simulation.

Compute the response characteristics using a final response value of 0.

s = lsiminfo(y,t,0)

s = struct with fields:
    SettlingTime: 22.8700
             Min: -0.4268
         MinTime: 2.0088
             Max: 0.2847
         MaxTime: 4.0733

You can plot the impulse response and verify these response characteristics. For example, the time at which the minimum response value (MinTime) is reached is approximately 2 seconds.

impulse(sys)