Shapiro–Shapiro conjecture for real pole placement

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Let m,p,nm,p,n be positive integers with n=mpn=mp. Let (Aˉ,Bˉ,Cˉ)(\bar{A},\bar{B},\bar{C}) be a minimal realization of the system represented through a coprime factorization D−1(s)N(s)D^{-1}(s)N(s), where the matrix [D(s)∣N(s)]\left[D(s)\mid N(s)\right] has the following form. The first row is

sm+p−1,sm+p−2,…,s2,s,1s^{m+p-1},s^{m+p-2},\ldots,s^2,s,1

and, for 1≤j<p1\leq j<p, the (j+1)(j+1)st row consists of the derivative of the jjth row divided by jj. Let d(m,p)d(m,p) be the corresponding enumerative degree, and let χ~(Aˉ,Bˉ,Cˉ)\tilde{\chi}_{(\bar{A},\bar{B},\bar{C})} denote the pole-placement map. Shapiro–Shapiro conjecture. The system is nondegenerate, and for any polynomial ϕˉ\bar{\phi} of degree mpmp with distinct real roots,

χ~(Aˉ,Bˉ,Cˉ)−1(ϕˉ)\tilde{\chi}_{(\bar{A},\bar{B},\bar{C})}^{-1}(\bar{\phi})

consists of exactly d(m,p)d(m,p) real solutions. This conjecture connects a special real pole-placement problem with questions in real algebraic geometry; its resolution is not stated in the supplied text.

References

Primary source

Joachim Rosenthal and Frank Sottile, “Some Remarks on Real and Complex Output Feedback”, arXiv:math/9702218 (1997).

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