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Nathan Mehlhop

Publications and source records attributed to Nathan Mehlhop.

4 recordsLinked to original sources
arXiv2023

Vector-valued maximal inequalities and multi-parameter oscillation inequalities for the polynomial ergodic averages along multi-dimensional subsets of primes

We prove the uniform $\ell^2$-valued maximal inequalities for polynomial ergodic averages and truncated singular operators of Cotlar type modeled over multi-dimensional subsets of primes. In the averages case, we combine this with earlier one-parameter oscillation estimates arXiv:2212.09874 to prove corresponding multi-parameter oscillation estimates. This provides a fuller quantitative description of the pointwise convergence of the mentioned averages and is a generalization of the polynomial Dunford-Zygmund ergodic theorem attributed to Bourgain arXiv:2209.01309. .

math.DS↗
arXiv2017

Lopsided Approximation of Amoebas

The amoeba of a Laurent polynomial is the image of the corresponding hypersurface under the coordinatewise log absolute value map. In this article, we demonstrate that a theoretical amoeba approximation method due to Purbhoo can be used efficiently in practice. To do this, we resolve the main bottleneck in Purbhoo's method by exploiting relations between cyclic resultants. We use the same approach to give an approximation of the Log preimage of the amoeba of a Laurent polynomial using semi-algebraic sets. We also provide a SINGULAR/SAGE implementation of these algorithms, which shows a significant speedup when our specialized cyclic resultant computation is used, versus a general purpose resultant algorithm.

cs.SC↗
arXiv2017

Expansion of permutations as products of transpositions

We compute the number of ways a given permutation can be written as a product of exactly $k$ transpositions. We express this number as a linear combination of explicit geometric sequences, with coefficients which can be computed in many particular cases. Along the way we prove several symmetry properties for matrices associated with bipartite graphs, as well as some general (likely known) properties of Young diagrams. The methods involve linear algebra, enumeration of border strip tableau, and a differential operator on symmetric polynomials.

math.CO↗