Stable Polynomial - Properties

Properties

  • The Routh-Hurwitz theorem provides an algorithm for determining if a given polynomial is Hurwitz stable.
  • To test if a given polynomial P (of degree d) is Schur stable, it suffices to apply this theorem to the transformed polynomial
 Q(z)=(z-1)^d P\left({{z+1}\over{z-1}}\right)

obtained after the Möbius transformation which maps the left half-plane to the open unit disc: P is Schur stable if and only if Q is Hurwitz stable.

  • Necessary condition: a Hurwitz stable polynomial (with real coefficients) has coefficients of the same sign (either all positive or all negative).
  • Sufficient condition: a polynomial with (real) coefficients such that:

is Schur stable.

  • Product rule: Two polynomials f and g are stable (of the same type) if and only if the product fg is stable.

Read more about this topic:  Stable Polynomial

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