ButterworthFilterModel

ButterworthFilterModel[n] creates a lowpass Butterworth filter of order n and cutoff frequency of 1.

ButterworthFilterModel[{n,ωc}] uses the cutoff frequency ωc.

ButterworthFilterModel[{"type",spec}] creates a filter of a given "type" using the specified parameters spec. 

ButterworthFilterModel[{"type",spec},var] expresses the model in terms of the variable var.

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