77 research outputs found
Arbitrary high-order linearly implicit energy-preserving algorithms for Hamiltonian PDEs
In this paper, we present a novel strategy to systematically construct
linearly implicit energy-preserving schemes with arbitrary order of accuracy
for Hamiltonian PDEs. Such novel strategy is based on the newly developed
exponential scalar variable (ESAV) approach that can remove the
bounded-from-blew restriction of nonlinear terms in the Hamiltonian functional
and provides a totally explicit discretization of the auxiliary variable
without computing extra inner products, which make it more effective and
applicable than the traditional scalar auxiliary variable (SAV) approach. To
achieve arbitrary high-order accuracy and energy preservation, we utilize the
symplectic Runge-Kutta method for both solution variables and the auxiliary
variable, where the values of internal stages in nonlinear terms are explicitly
derived via an extrapolation from numerical solutions already obtained in the
preceding calculation. A prediction-correction strategy is proposed to further
improve the accuracy. Fourier pseudo-spectral method is then employed to obtain
fully discrete schemes. Compared with the SAV schemes, the solution variables
and the auxiliary variable in these ESAV schemes are now decoupled. Moreover,
when the linear terms are of constant coefficients, the solution variables can
be explicitly solved by using the fast Fourier transform. Numerical experiments
are carried out for three Hamiltonian PDEs to demonstrate the efficiency and
conservation of the ESAV schemes
Two novel classes of arbitrary high-order structure-preserving algorithms for canonical Hamiltonian systems
In this paper, we systematically construct two classes of
structure-preserving schemes with arbitrary order of accuracy for canonical
Hamiltonian systems. The one class is the symplectic scheme, which contains two
new families of parameterized symplectic schemes that are derived by basing on
the generating function method and the symmetric composition method,
respectively. Each member in these schemes is symplectic for any fixed
parameter. A more general form of generating functions is introduced, which
generalizes the three classical generating functions that are widely used to
construct symplectic algorithms. The other class is a novel family of energy
and quadratic invariants preserving schemes, which is devised by adjusting the
parameter in parameterized symplectic schemes to guarantee energy conservation
at each time step. The existence of the solutions of these schemes is verified.
Numerical experiments demonstrate the theoretical analysis and conservation of
the proposed schemes
Improved Noisy Student Training for Automatic Speech Recognition
Recently, a semi-supervised learning method known as "noisy student training"
has been shown to improve image classification performance of deep networks
significantly. Noisy student training is an iterative self-training method that
leverages augmentation to improve network performance. In this work, we adapt
and improve noisy student training for automatic speech recognition, employing
(adaptive) SpecAugment as the augmentation method. We find effective methods to
filter, balance and augment the data generated in between self-training
iterations. By doing so, we are able to obtain word error rates (WERs)
4.2%/8.6% on the clean/noisy LibriSpeech test sets by only using the clean 100h
subset of LibriSpeech as the supervised set and the rest (860h) as the
unlabeled set. Furthermore, we are able to achieve WERs 1.7%/3.4% on the
clean/noisy LibriSpeech test sets by using the unlab-60k subset of LibriLight
as the unlabeled set for LibriSpeech 960h. We are thus able to improve upon the
previous state-of-the-art clean/noisy test WERs achieved on LibriSpeech 100h
(4.74%/12.20%) and LibriSpeech (1.9%/4.1%).Comment: 5 pages, 5 figures, 4 tables; v2: minor revisions, reference adde
Multi-Dialect Speech Recognition With A Single Sequence-To-Sequence Model
Sequence-to-sequence models provide a simple and elegant solution for
building speech recognition systems by folding separate components of a typical
system, namely acoustic (AM), pronunciation (PM) and language (LM) models into
a single neural network. In this work, we look at one such sequence-to-sequence
model, namely listen, attend and spell (LAS), and explore the possibility of
training a single model to serve different English dialects, which simplifies
the process of training multi-dialect systems without the need for separate AM,
PM and LMs for each dialect. We show that simply pooling the data from all
dialects into one LAS model falls behind the performance of a model fine-tuned
on each dialect. We then look at incorporating dialect-specific information
into the model, both by modifying the training targets by inserting the dialect
symbol at the end of the original grapheme sequence and also feeding a 1-hot
representation of the dialect information into all layers of the model.
Experimental results on seven English dialects show that our proposed system is
effective in modeling dialect variations within a single LAS model,
outperforming a LAS model trained individually on each of the seven dialects by
3.1 ~ 16.5% relative.Comment: submitted to ICASSP 201
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