Shapiro–Shapiro conjecture for totally positive flags

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Let m,p>1m,p>1, let Grass⁡(p,m+p)\operatorname{Grass}(p,m+p) be the Grassmannian, and let α1,…,αn\alpha^1,\ldots,\alpha^n be Schubert data. A real upper-triangular matrix with diagonal entries 11 is totally positive when every minor not forced to vanish by triangularity is positive; this induces an order F1<⋯<FnF^1<\cdots<F^n on real complete flags. Shapiro–Shapiro conjecture. If F1<⋯<FnF^1<\cdots<F^n are real flags, then the Schubert varieties Ωα1F1,…,ΩαnFn\Omega_{\alpha^1}F^1,\ldots,\Omega_{\alpha^n}F^n intersect transversally, and all points of the intersection are real. The conjecture generalizes the osculating-flag construction to totally positive flags; the paper proves the first nontrivial instance and gives computational evidence, but does not establish the general claim.

References

Primary source

Frank Sottile, “Real Schubert Calculus: Polynomial systems and a conjecture of Shapiro and Shapiro”, arXiv:math/9904138 (1999).

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