Synthetic parametric model

Introduction

On this page you will find a purely synthetic parametric model. The goal is to have a simple parametric model which one can use to experiment with different system orders, parameter values etc.

System description

The parameter $\epsilon$ scales the real part of the system poles, that is, $p_k=\epsilon a_k+j{b}_k$. If the system is in pole-residue form, then

$H(s)=\sum _{i=1}^n\frac{r_i}{s-p_i}=\sum _{i=1}^n\frac{r_i}{s-(\epsilon a_i+j{b}_i)},$

which has the state-space realisation

$\hat{A}=\epsilon \left[\begin{array}{ccc}{a}_1& & \\ & \ddots & \\ & & a_n\end{array}\right]+\left[\begin{array}{ccc}j{b}_1& & \\ & \ddots & \\ & & j{b}_n\end{array}\right]=\epsilon {\hat{A}}_{\epsilon }+{\hat{A}}_0,$

$\hat{B}=[1,\dots ,1{]}^T,\hat{C}=[r_1,\dots ,r_n],D=0.$

Notice that the system matrices have complex entries.

For simplicity, assume that $n$ is even, $n=2k$, and that all system poles are complex and ordered in complex conjugate pairs, i.e.

$p_1=\epsilon a_1+j{b}_1,p_2=\epsilon a_1-j{b}_1,\dots ,p_{n-1}=\epsilon a_k+j{b}_k,p_n=\epsilon a_k-j{b}_k.$

Which also implies that the residues form complex conjugate pairs $r_1,{\overline{r}}_1,\dots ,r_k,{\overline{r}}_k.$

Then a realization with matrices having real entries is given by

$A=T\hat{A}{T}^{*},B=T\hat{B},C=\hat{C}{T}^{*},D=0,$

with $T=\left[\begin{array}{ccc}{T}_0& & \\ & \ddots & \\ & & T_0\end{array}\right]$, for $T_0=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& -j\\ 1& j\end{array}\right]$.