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