6,384 research outputs found
On error-spectrum shaping in state-space digital filters
A new scheme for shaping the error spectrum in state-space digital filter structures is proposed. The scheme is based on the application of diagonal second-order error feedback, and can be used in any arbitrary state-space structure having arbitrary order. A method to obtain noise-optimal state-space structures for fixed error feedback coefficients, starting from noise optimal structures in absence of error feedback (the Mullis and Roberts Structures), is also outlined. This optimization is based on the theory of continuous equivalence for state-space structures
Knowledge-based intelligent error feedback in a Spanish ICALL system
This paper describes the Spanish ICALL system ESPADA
which helps language learners to improve their syntactical
knowledge. The most important parts of ESPADA for the learner are a Demonstration Module and an Analysis Module. The Demonstration Module provides animated presentation of selected grammatical information. The Analysis Module is able to parse ill-formed sentences and to give adequate feedback on 28 different error types from different levels of language use (syntax, semantics, agreement). It contains a robust chart-based island parser which uses a combination
of mal-rules and constraint relaxation to ensure that learner input can be analysed and appropriate error feedback can be generated
Visuomotor Learning Enhanced by Augmenting Instantaneous Trajectory Error Feedback during Reaching
We studied reach adaptation to a 30u visuomotor rotation to determine whether augmented error feedback can promote faster and more complete motor learning. Four groups of healthy adults reached with their unseen arm to visual targets surrounding a central starting point. A manipulandum tracked hand motion and projected a cursor onto a display immediately above the horizontal plane of movement. For one group, deviations from the ideal movement were amplified with a gain of 2 whereas another group experienced a gain of 3.1. The third group experienced an offset equal to the average error seen in the initial perturbations, while a fourth group served as controls. Learning in the gain 2 and offset groups was nearly twice as fast as controls. Moreover, the offset group averaged more reduction in error. Such error augmentation techniques may be useful for training novel visuomotor transformations as required of robotic teleoperators or in movement rehabilitation of the neurologically impaired
Momentum Provably Improves Error Feedback!
Due to the high communication overhead when training machine learning models
in a distributed environment, modern algorithms invariably rely on lossy
communication compression. However, when untreated, the errors caused by
compression propagate, and can lead to severely unstable behavior, including
exponential divergence. Almost a decade ago, Seide et al [2014] proposed an
error feedback (EF) mechanism, which we refer to as EF14, as an immensely
effective heuristic for mitigating this issue. However, despite steady
algorithmic and theoretical advances in the EF field in the last decade, our
understanding is far from complete. In this work we address one of the most
pressing issues. In particular, in the canonical nonconvex setting, all known
variants of EF rely on very large batch sizes to converge, which can be
prohibitive in practice. We propose a surprisingly simple fix which removes
this issue both theoretically, and in practice: the application of Polyak's
momentum to the latest incarnation of EF due to Richt\'{a}rik et al. [2021]
known as EF21. Our algorithm, for which we coin the name EF21-SGDM, improves
the communication and sample complexities of previous error feedback algorithms
under standard smoothness and bounded variance assumptions, and does not
require any further strong assumptions such as bounded gradient dissimilarity.
Moreover, we propose a double momentum version of our method that improves the
complexities even further. Our proof seems to be novel even when compression is
removed from the method, and as such, our proof technique is of independent
interest in the study of nonconvex stochastic optimization enriched with
Polyak's momentum
Clip21: Error Feedback for Gradient Clipping
Motivated by the increasing popularity and importance of large-scale training
under differential privacy (DP) constraints, we study distributed gradient
methods with gradient clipping, i.e., clipping applied to the gradients
computed from local information at the nodes. While gradient clipping is an
essential tool for injecting formal DP guarantees into gradient-based methods
[1], it also induces bias which causes serious convergence issues specific to
the distributed setting. Inspired by recent progress in the error-feedback
literature which is focused on taming the bias/error introduced by
communication compression operators such as Top- [2], and mathematical
similarities between the clipping operator and contractive compression
operators, we design Clip21 -- the first provably effective and practically
useful error feedback mechanism for distributed methods with gradient clipping.
We prove that our method converges at the same
rate as distributed gradient descent in
the smooth nonconvex regime, which improves the previous best
rate which was obtained under
significantly stronger assumptions. Our method converges significantly faster
in practice than competing methods
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