913 research outputs found
Self-Learning Monte Carlo Method
Monte Carlo simulation is an unbiased numerical tool for studying classical
and quantum many-body systems. One of its bottlenecks is the lack of general
and efficient update algorithm for large size systems close to phase transition
or with strong frustrations, for which local updates perform badly. In this
work, we propose a new general-purpose Monte Carlo method, dubbed self-learning
Monte Carlo (SLMC), in which an efficient update algorithm is first learned
from the training data generated in trial simulations and then used to speed up
the actual simulation. We demonstrate the efficiency of SLMC in a spin model at
the phase transition point, achieving a 10-20 times speedup.Comment: add more refs and correct some typo
PiCANet: Learning Pixel-wise Contextual Attention for Saliency Detection
Contexts play an important role in the saliency detection task. However,
given a context region, not all contextual information is helpful for the final
task. In this paper, we propose a novel pixel-wise contextual attention
network, i.e., the PiCANet, to learn to selectively attend to informative
context locations for each pixel. Specifically, for each pixel, it can generate
an attention map in which each attention weight corresponds to the contextual
relevance at each context location. An attended contextual feature can then be
constructed by selectively aggregating the contextual information. We formulate
the proposed PiCANet in both global and local forms to attend to global and
local contexts, respectively. Both models are fully differentiable and can be
embedded into CNNs for joint training. We also incorporate the proposed models
with the U-Net architecture to detect salient objects. Extensive experiments
show that the proposed PiCANets can consistently improve saliency detection
performance. The global and local PiCANets facilitate learning global contrast
and homogeneousness, respectively. As a result, our saliency model can detect
salient objects more accurately and uniformly, thus performing favorably
against the state-of-the-art methods
Self-Learning Monte Carlo Method in Fermion Systems
We develop the self-learning Monte Carlo (SLMC) method, a general-purpose
numerical method recently introduced to simulate many-body systems, for
studying interacting fermion systems. Our method uses a highly-efficient update
algorithm, which we design and dub "cumulative update", to generate new
candidate configurations in the Markov chain based on a self-learned bosonic
effective model. From general analysis and numerical study of the double
exchange model as an example, we find the SLMC with cumulative update
drastically reduces the computational cost of the simulation, while remaining
statistically exact. Remarkably, its computational complexity is far less than
the conventional algorithm with local updates
Self-Learning Determinantal Quantum Monte Carlo Method
Self-learning Monte Carlo method [arXiv:1610.03137, 1611.09364] is a powerful
general-purpose numerical method recently introduced to simulate many-body
systems. In this work, we implement this method in the framework of
determinantal quantum Monte Carlo simulation of interacting fermion systems.
Guided by a self-learned bosonic effective action, our method uses a cumulative
update [arXiv:1611.09364] algorithm to sample auxiliary field configurations
quickly and efficiently. We demonstrate that self-learning determinantal Monte
Carlo method can reduce the auto-correlation time to as short as one near a
critical point, leading to -fold speedup. This enables to
simulate interacting fermion system on a lattice for the first
time, and obtain critical exponents with high accuracy.Comment: 5 pages, 4 figure
Weak Topological Insulators in PbTe/SnTe Superlattices
It is desirable to realize topological phases in artificial structures by
engineering electronic band structures. In this paper, we investigate
superlattices along [001] direction and find a robust
weak topological insulator phase for a large variety of layer numbers m and
2n-m. We confirm this topologically non-trivial phase by calculating Z2
topological invariants and topological surface states based on the
first-principles calculations. We show that the folding of Brillouin zone due
to the superlattice structure plays an essential role in inducing topologically
non-trivial phases in this system. This mechanism can be generalized to other
systems in which band inversion occurs at multiple momenta, and gives us a
brand-new way to engineer topological materials in artificial structures.Comment: 6 pages, 4 figures, another author adde
Self-Learning Monte Carlo Method: Continuous-Time Algorithm
The recently-introduced self-learning Monte Carlo method is a general-purpose
numerical method that speeds up Monte Carlo simulations by training an
effective model to propose uncorrelated configurations in the Markov chain. We
implement this method in the framework of continuous time Monte Carlo method
with auxiliary field in quantum impurity models. We introduce and train a
diagram generating function (DGF) to model the probability distribution of
auxiliary field configurations in continuous imaginary time, at all orders of
diagrammatic expansion. By using DGF to propose global moves in configuration
space, we show that the self-learning continuous-time Monte Carlo method can
significantly reduce the computational complexity of the simulation.Comment: 6 pages, 5 figures + 2 page supplemental materials, to be published
in Phys. Rev. B Rapid communication sectio
Study on Risk Zoning Technology of Major Environmental Risk Sources in Urban Scale and Its Application in Shanghai, China
AbstractBecause of the inherent characteristics of the cities, such as high population density, complicated traffic, numerous pollution sources, etc., it has become very important to conduct environmental risk zoning in urban scale. Based on analyzing the current research situation of the regional environmental risk assessment and regional environmental risk zoning, this paper constructed the index system and the quantitative model of environmental risk zoning which are fit for urban scale, applies AHP to weight index and comprehensive evaluation method to calculate comprehensive risk index value. Then applying the method to Shanghai, and with the clustering function of SPSS and the visualization of GIS, the quantitative risk zoning map of Shanghai was obtained. The result can provide reference for environmental risk management of Shanghai
Accelerating Diffusion-based Combinatorial Optimization Solvers by Progressive Distillation
Graph-based diffusion models have shown promising results in terms of
generating high-quality solutions to NP-complete (NPC) combinatorial
optimization (CO) problems. However, those models are often inefficient in
inference, due to the iterative evaluation nature of the denoising diffusion
process. This paper proposes to use progressive distillation to speed up the
inference by taking fewer steps (e.g., forecasting two steps ahead within a
single step) during the denoising process. Our experimental results show that
the progressively distilled model can perform inference 16 times faster with
only 0.019% degradation in performance on the TSP-50 dataset
Symmetry Enforced Self-Learning Monte Carlo Method Applied to the Holstein Model
Self-learning Monte Carlo method (SLMC), using a trained effective model to
guide Monte Carlo sampling processes, is a powerful general-purpose numerical
method recently introduced to speed up simulations in (quantum) many-body
systems. In this work, we further improve the efficiency of SLMC by enforcing
physical symmetries on the effective model. We demonstrate its effectiveness in
the Holstein Hamiltonian, one of the most fundamental many-body descriptions of
electron-phonon coupling. Simulations of the Holstein model are notoriously
difficult due to the combination of the typical cubic scaling of fermionic
Monte Carlo and the presence of extremely long autocorrelation times. Our
method addresses both bottlenecks. This enables simulations on large lattices
in the most difficult parameter regions, and evaluation of the critical point
for the charge density wave transition at half-filling with high precision. We
argue that our work opens a new research area of quantum Monte Carlo (QMC),
providing a general procedure to deal with ergodicity in situations involving
Hamiltonians with multiple, distinct low energy states.Comment: 4 pages, 3 figures with 2 pages supplemental materia
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