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Namespace: frest

Create step input signal


A step input signal has an initial value of 0 and transitions to a specified step size value after a specified step time. When performing frequency response estimation, step inputs are quick to simulate and can be useful as a first try when you do not have much knowledge about the system you are trying to estimate. However, the amplitude of the excitation decreases rapidly with increasing frequency. Therefore, step signals are best used to identify low-order plants where the slowest poles are dominant. Step inputs are not recommended for estimation across a wide range of frequencies.

When you use a step input signal for estimation, the frequencies returned in the estimated frd model depend on the length and sampling time of the signal. They are the frequencies obtained in the fast Fourier transform of the input signal (see the Algorithm section of frestimate).

For more information on input signals for frequency response estimation, see Estimation Input Signals.


input = frest.createStep(Name,Value) creates a step input signal for frequency response estimation using options specified using one or more name-value pair arguments.


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Create a step input signal with a default sample time and the following properties:

  • Step time of 5 seconds

  • Step size of 0.1

  • Total duration of 15 seconds

input = frest.createStep('StepTime',5,'StepSize',0.1,'FinalTime',15)

  Common Properties:
            Name: 'Created with frest.createStep utility'
            Time: [15001x1 double]
        TimeInfo: tsdata.timemetadata
            Data: [15001x1 double]
        DataInfo: tsdata.datametadata

Plot the step signal.


Input Arguments

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Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: 'Ts',0.01 sets the input signal sample time to 0.01

Sample time of the input signal in seconds, specified as the comma-separated pair 'Ts', followed by a positive scalar.

Step time when the input signal transitions from 0 to StepSize, specified as the comma-separated pair 'StepTime' followed by a positive scalar.

StepTime must be less than FinalTime

Step size, specified as the comma-separated pair 'StepSize' followed by a nonzero scalar. The input signal has value StepSize after StepTime seconds.

Input signal duration in seconds, specified as the comma-separated pair 'FinalTime' followed by a positive scalar.

FinalTime must be greater than StepTime

Output Arguments

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Step input signal for frequency response estimation, returned as a timeseries object.

To view a plot of your input signal, type plot(input).

Version History

Introduced in R2009b