The Stratified Spaces of Real Polynomials & Trajectory Spaces of Traversing Flows

This paper is the third in a series that researches the Morse Theory, gradient flows, concavity and complexity on smooth compact manifolds with boundary. Employing the local analytic models from \cite{K2}, for \emph{traversally generic flows} on $(n+1)$-manifolds $X$, we embark on a detailed and somewhat tedious study of universal combinatorics of their tangency patterns with respect to the boundary $\text{d}X$. This combinatorics is captured by a universal poset ${\mathrm{\Omega }}_{{}^{\mathrm{\prime }}⟨n]}^{\bullet }$ which depends only on the dimension of $X$. It is intimately linked with the combinatorial patterns of real divisors of real polynomials in one variable of degrees which do not exceed $2(n+1)$. Such patterns are elements of another natural poset ${\mathrm{\Omega }}_{⟨2n+2]}$ that describes the ways in which the real roots merge, divide, appear, and disappear under deformations of real polynomials. The space of real degree $d$ polynomials ${\mathcal{P}}^d$ is stratified so that its pure strata are cells, labelled by the elements of the poset ${\mathrm{\Omega }}_{⟨d]}$. This cellular structure in ${\mathcal{P}}^d$ is interesting on its own right (see Theorem \ref {th4.1} and Theorem \ref {th4.2}). Moreover, it helps to understand the \emph{localized} structure of the trajectory spaces $\mathcal T(v)$fortraversallygenericfields$v$, the main subject of Theorem \ref {th5.2} and Theorem \ref {th5.3}.