Hello,
Check out the following quoted comment from Maria Sabrina Sarto (at the end of one of the rationalfit() references: Gustavsen.B and A.Semlyen, “Rational approximation of frequency domain responses by vector fitting,” IEEE Trans. Power Delivery, Vol. 14, No. 3, pp. 1052–1061, July 1999)
"It can be also considered as a general approach to compute numerically the inverse Fourier transform of functions describing electromagnetic systems in the frequency domain. In fact, these functions are often characterized by very broad frequency spectra; they can be either smooth functions or can have many resonance peaks, so that the calculation of their discrete inverse Fourier transform can be expensive and inefficient"
Here "It" can be interpreted as using rationalfit() to get the rational function object which is supplied to timeresp(), along with an input time series, to effectively calculate the discrete inverse Fourier transform.
The rational fit guarantees stability and causality of the response but not necessarily passivity. Check out: https://nl.mathworks.com/help/rf/ug/passivity-test-visualize-and-enforce-passivity-of-ratioanlfir-output.html
Hope this helps,
Max
