The monotonicity conjecture for LGL interval quotients

Let ξ0N<ξ1N<<ξNN\xi^N_0<\xi^N_1<\cdots<\xi^N_N be the LGL points, let ΔkN=[ξkN,ξk+1N]\Delta^N_k=[\xi^N_k,\xi^N_{k+1}], and define qkN=ΔkN/Δk1Nq_k^N=|\Delta^N_k|/|\Delta^N_{k-1}| for the relevant indices. The family has property MQNˉ\mathbf{MQ}_{\bar N} if qkNqkN+1q_k^N\leq q_k^{N+1} for N<NˉN<\bar N and fixed kk, and qkNqk+1Nq_k^N\geq q_{k+1}^N for 1k(N3)/21\leq k\leq\lfloor(N-3)/2\rfloor and NNˉN\leq\bar N. The LGL quotient monotonicity conjecture. The LGL grids have property MQNˉ\mathbf{MQ}_{\bar N} for every NˉN\bar N\in\mathbb{N}. Numerical evidence verifies the property through Nˉ=2000\bar N=2000; its validity for all orders remains open.

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Primary source

Kolja Brix, Claudio Canuto and Wolfgang Dahmen, “Legendre-Gauss-Lobatto grids and associated nested dyadic grids”, arXiv:1311.0028 (2013).

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