Models

Benchmark Model Templates

This page specifies templates for the types of models used as benchmark systems. In particular, the naming schemes established here are used in the corresponding data sets for all benchmarks. For example, $A$ always serves as the name of the component matrix applied to the state $x(t)$ in a linear time-invariant system. For all models we assume an input $u : \mathbb{R} \to \mathbb{R}^m$, with components $u_j, j = 1, \ldots, m$, a state $x : \mathbb{R} \to \mathbb{R}^n$, and an output $y : \mathbb{R} \to \mathbb{R}^q$. For all parametric models, we assume each component has $\ell$ parameters; in cases where a component has fewer than $\ell$ parameters, the extras are treated as $0$. Some benchmarks (e.g., Bone Model) have a constant forcing term, in which case, it is assumed that $u(t)$ is identically $1$.

Linear Time-Invariant First-Order System (LTI-FOS)

$\begin{align} E\dot{x}(t) &= Ax(t) + Bu(t),\\ y(t) &= Cx(t) + Du(t), \end{align}$

with

$E \in \mathbb{R}^{n \times n}$, $A \in \mathbb{R}^{n \times n}$, $B \in \mathbb{R}^{n \times m}$, $C \in \mathbb{R}^{q \times n}$, $D \in \mathbb{R}^{q \times m}$.

Linear Time-Varying First-Order System (LTV-FOS)

$\begin{align} E(t)\dot{x}(t) &= A(t)x(t) + B(t)u(t),\\ y(t) &= C(t)x(t) + D(t)u(t), \end{align}$

with

$E : \mathbb{R} \to \mathbb{R}^{n \times n}$, $A : \mathbb{R} \to \mathbb{R}^{n \times n}$, $B : \mathbb{R} \to \mathbb{R}^{n \times m}$, $C : \mathbb{R} \to \mathbb{R}^{q \times n}$, $D : \mathbb{R} \to \mathbb{R}^{q \times m}$.

Affine Parametric LTI-FOS (AP-LTI-FOS)

$\begin{align} (E + \sum_{i=1}^{\ell} p^E_i E_i)\dot{x}(t) &= (A + \sum_{i=1}^{\ell} p^A_i A_i) x(t) + (B + \sum_{i=1}^{\ell} p^B_i B_i)u(t),\\ y(t) &= (C + \sum_{i=1}^{\ell} p^C_i C_i)x(t), \end{align}$

with

$E, E_i \in \mathbb{R}^{n \times n}$; $A, A_i \in \mathbb{R}^{n \times n}$; $B, B_i \in \mathbb{R}^{n \times m}$; and $C, C_i \in \mathbb{R}^{q \times n}$, for all $i = 1, \ldots, \ell$.

Linear Time-Invariant Second-Order System (LTI-SOS)

$\begin{align} M \ddot{x}(t) + E \dot{x}(t) + K x(t) &= B u(t), \\ y(t) &= C_p x(t) + C_v \dot{x}(t) + D u(t), \end{align}$

with

$M \in \mathbb{R}^{n \times n}$, $E \in \mathbb{R}^{n \times n}$, $K \in \mathbb{R}^{n \times n}$, $B \in \mathbb{R}^{n \times m}$, $C_p, C_v \in \mathbb{R}^{q \times n}$, $D \in \mathbb{R}^{q \times m}$.

When $C_v = 0$, we denote $C = C_p$.

Affine Parametric LTI-SOS (AP-LTI-SOS)

$\begin{align} (M + \sum_{i=1}^{\ell} p^M_i M_i)\ddot{x}(t) + (E + \sum_{i=1}^{\ell} p^E_i E_i)\dot{x}(t) + (K + \sum_{i=1}^{\ell} p^K_i K_i)x(t) &= (B + \sum_{i=1}^{\ell} p^B_i B_i) u(t), \\ y(t) &= (C + \sum_{i=1}^{\ell} p^C_i C_i) x(t), \end{align}$

with

$M, M_i \in \mathbb{R}^{n \times n}$; $E, E_i \in \mathbb{R}^{n \times n}$; $K, K_i \in \mathbb{R}^{n \times n}$; $B, B_i \in \mathbb{R}^{n \times m}$; and $C, C_i \in \mathbb{R}^{q \times n}$, for all $i = 1, \ldots, \ell$.

Quadratic-Bilinear System (QBS)

$\begin{align} E\dot{x}(t) &= A x(t) + H x(t) \otimes x(t) + \sum_{j=1}^m N_j x(t) u_j(t) + B u(t), \\ y(t) &= Cx(t) + Du(t), \end{align}$

with

$E \in \mathbb{R}^{n \times n}$, $A \in \mathbb{R}^{n \times n}$, $H \in \mathbb{R}^{n \times n^2}$, $N_j \in \mathbb{R}^{n \times n}$, $B \in \mathbb{R}^{n \times m}$, $C \in \mathbb{R}^{q \times n}$, $D \in \mathbb{R}^{q \times m}$.

Nonlinear Time-Invariant First-Order System (NLTI-FOS)

$\begin{align} E\dot{x}(t) &= Ax(t) + f(x(t),u(t)) + Bu(t),\\ y(t) &= Cx(t) + Du(t), \end{align}$

with

$E \in \mathbb{R}^{n \times n}$, $A \in \mathbb{R}^{n \times n}$, $B \in \mathbb{R}^{n \times m}$, $C \in \mathbb{R}^{q \times n}$, $D \in \mathbb{R}^{q \times m}$, $f : \mathbb{R}^n \times \mathbb{R}^m \to \mathbb{R}^n$.

Nonlinear Time-Invariant Second-Order System (NLTI-SOS)

$\begin{align} M \ddot{x}(t) + E \dot{x}(t) + K x(t) &= B u(t) + F f(x(t),u(t)), \\ y(t) &= C_p x(t) + C_v \dot{x}(t) + D u(t), \end{align}$

with

$M \in \mathbb{R}^{n \times n}$, $E \in \mathbb{R}^{n \times n}$, $K \in \mathbb{R}^{n \times n}$, $B \in \mathbb{R}^{n \times m}$, $F \in \mathbb{R}^{n \times n}$, $C_p, C_v \in \mathbb{R}^{q \times n}$, $D \in \mathbb{R}^{q \times m}$, $f : \mathbb{R}^n \times \mathbb{R}^m \to \mathbb{R}^n$.

When $C_v = 0$, we denote $C = C_p$.