Liénard–Chipart criterion

The Routh–Hurwitz stability criterion says that a necessary and sufficient condition for all the roots of the polynomial with real coefficients

${\displaystyle f(z)=a_{0}z^{n}+a_{1}z^{n-1}+\cdots +a_{n}\,(a_{0}>0)}$

to have negative real parts (i.e. ${\displaystyle f}$ is Hurwitz stable) is that

${\displaystyle \Delta _{1}>0,\,\Delta _{2}>0,\ldots ,\Delta _{n}>0,}$

where ${\displaystyle \Delta _{i}}$ is the i-th leading principal minor of the Hurwitz matrix associated with ${\displaystyle f}$.

Using the same notation as above, the Liénard–Chipart criterion is that ${\displaystyle f}$ is Hurwitz-stable if and only if any one of the four conditions is satisfied:

1. ${\displaystyle a_{n}>0,a_{n-2}>0,\ldots$ ;\,\Delta _{1}>0,\Delta _{3}>0,\ldots }
2. ${\displaystyle a_{n}>0,a_{n-2}>0,\ldots$ ;\,\Delta _{2}>0,\Delta _{4}>0,\ldots }
3. ${\displaystyle a_{n}>0,a_{n-1}>0,a_{n-3}>0,\ldots$ ;\,\Delta _{1}>0,\Delta _{3}>0,\ldots }
4. ${\displaystyle a_{n}>0,a_{n-1}>0,a_{n-3}>0,\ldots$ ;\,\Delta _{2}>0,\Delta _{4}>0,\ldots }

Hence one can see that by choosing one of these conditions, the number of determinants required to be evaluated is reduced.

• "Liénard–Chipart criterion", Encyclopedia of Mathematics, EMS Press, 2001 [1994]