Duistermaat index is a symplectic invariant defined for triples of Lagrangian subspaces. We discuss its concise axiomatic definition, its relation to the Maslov index of paths of Lagrangian subspaces and its surprising application to eigenvalue interlacing for differential operators with different sets of boundary conditions.
Based on joint work with Graham Cox, Yuri Latushkin and Selim Sukhtaiev.
Duistermaat index and its application to eigenvalue interlacing
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