= Proper rational transfer function
{title2=$G(s)=N(s)/D(s),\quad\deg N\le\deg D$}
A <proper rational transfer function> is a <rational function> whose numerator <polynomial> has <polynomial degree> no greater than its denominator <polynomial>, after common factors are canceled. Every finite-dimensional continuous-time <linear time-invariant system> of the form $\dot x=Ax+Bu$, $y=Cx+Du$ has such a <transfer function> $G(s)=C(sI-A)^{-1}B+D$. https://ocw.mit.edu/courses/6-241j-dynamic-systems-and-control-spring-2011/996025f6db0d90b00f11c44fc49b85f9_MIT6_241JS11_textbook.pdf[Dahleh, Dahleh and Verghese, Lectures on Dynamic Systems and Control, section 15.3.1]{ref}
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