Select frequency points or range in FRD model
subsys = fselect(sys,fmin,fmax)
subsys = fselect(sys,index)
subsys = fselect(sys,fmin,fmax) takes an
FRD model sys and selects the portion of the frequency response between
the frequencies fmin and fmax.
The selected range [fmin,fmax] should be expressed
in the FRD model units. For an IDFRD model,
the SpectrumData, CovarianceData and NoiseCovariance values,
if non-empty, are also selected in the chosen range.
subsys = fselect(sys,index) selects the
frequency points specified by the vector of indices index. The resulting
frequency grid is
sys.Frequency(index)