51 research outputs found
On the sign-imbalance of partition shapes
Let the sign of a standard Young tableau be the sign of the permutation you
get by reading it row by row from left to right, like a book. A conjecture by
Richard Stanley says that the sum of the signs of all SYTs with n squares is
2^[n/2]. We present a stronger theorem with a purely combinatorial proof using
the Robinson-Schensted correspondence and a new concept called chess tableaux.
We also prove a sharpening of another conjecture by Stanley concerning
weighted sums of squares of sign-imbalances. The proof is built on a remarkably
simple relation between the sign of a permutation and the signs of its
RS-corresponding tableaux.Comment: 12 pages. Better presentatio
Making multigraphs simple by a sequence of double edge swaps
We show that any loopy multigraph with a graphical degree sequence can be
transformed into a simple graph by a finite sequence of double edge swaps with
each swap involving at least one loop or multiple edge. Our result answers a
question of Janson motivated by random graph theory, and it adds to the rich
literature on reachability of double edge swaps with applications in Markov
chain Monte Carlo sampling from the uniform distribution of graphs with
prescribed degrees.Comment: 13 page
Learning to Personalize in Appearance-Based Gaze Tracking
Personal variations severely limit the performance of appearance-based gaze
tracking. Adapting to these variations using standard neural network model
adaptation methods is difficult. The problems range from overfitting, due to
small amounts of training data, to underfitting, due to restrictive model
architectures. We tackle these problems by introducing the SPatial Adaptive
GaZe Estimator (SPAZE). By modeling personal variations as a low-dimensional
latent parameter space, SPAZE provides just enough adaptability to capture the
range of personal variations without being prone to overfitting. Calibrating
SPAZE for a new person reduces to solving a small optimization problem. SPAZE
achieves an error of 2.70 degrees with 9 calibration samples on MPIIGaze,
improving on the state-of-the-art by 14 %. We contribute to gaze tracking
research by empirically showing that personal variations are well-modeled as a
3-dimensional latent parameter space for each eye. We show that this
low-dimensionality is expected by examining model-based approaches to gaze
tracking. We also show that accurate head pose-free gaze tracking is possible
Correlation Effects in Orbital Magnetism
Orbital magnetization is known empirically to play an important role in
several magnetic phenomena, such as permanent magnetism and ferromagnetic
superconductivity. Within the recently developed ''modern theory of orbital
magnetization'', theoretical insight has been gained into the nature of this
often neglected contribution to magnetism, but is based on an underlying
mean-field approximation. From this theory, a few treatments have emerged which
also take into account correlations beyond the mean-field approximation. Here,
we apply the scheme developed in a previous work [Phys. Rev. B , 161104(R) (2016)] to the Haldane-Hubbard model to investigate the
effect of charge fluctuations on the orbital magnetization within the
approximation. Qualitatively, we are led to distinguish between two quite
different situations: (i) When the lattice potential is larger than the nearest
neighbor hopping, the correlations are found to boost the orbital
magnetization. (ii) If the nearest neighbor hopping is instead larger than the
lattice potential, the correlations reduce the magnetization.Comment: 8 pages, 9 figure
From Bruhat intervals to intersection lattices and a conjecture of Postnikov
We prove the conjecture of A. Postnikov that (A) the number of regions in the
inversion hyperplane arrangement associated with a permutation w\in \Sn is at
most the number of elements below in the Bruhat order, and (B) that
equality holds if and only if avoids the patterns 4231, 35142, 42513 and
351624. Furthermore, assertion (A) is extended to all finite reflection groups.
A byproduct of this result and its proof is a set of inequalities relating
Betti numbers of complexified inversion arrangements to Betti numbers of closed
Schubert cells. Another consequence is a simple combinatorial interpretation of
the chromatic polynomial of the inversion graph of a permutation which avoids
the above patterns.Comment: 24 page
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