22 research outputs found
Momentum-Based Variance Reduction in Non-Convex SGD
Variance reduction has emerged in recent years as a strong competitor to
stochastic gradient descent in non-convex problems, providing the first
algorithms to improve upon the converge rate of stochastic gradient descent for
finding first-order critical points. However, variance reduction techniques
typically require carefully tuned learning rates and willingness to use
excessively large "mega-batches" in order to achieve their improved results. We
present a new algorithm, STORM, that does not require any batches and makes use
of adaptive learning rates, enabling simpler implementation and less
hyperparameter tuning. Our technique for removing the batches uses a variant of
momentum to achieve variance reduction in non-convex optimization. On smooth
losses , STORM finds a point with in iterations
with variance in the gradients, matching the optimal rate but
without requiring knowledge of .Comment: Added Ac
Design and Calibration of Pinch Force Measurement Using Strain Gauge for Post-Stroke Patients
Two fingers strength is an indicative measurement of pinch impairment. Conventionally, Fugl Meyer Upper Extremity Assessment (FMA-UE) is the primary standard to measure pinch strength of post-stroke survivors. In literature, the evaluation method performed by the therapist is subjective and exposed to inter-rater and intra-rater reliabilities. Recently, force-sensing resistors were implemented to measure two fingers force, but these sensors are subjected to nonlinearity, high hysteresis, and voltage drift. This paper presents a design of pinch force measurement based on the strain gauge. The pinch sensor was calibrated within a range of between 0 N to 50 N over a pinching length of 20 mm with a linearity error of 0.0123% and hysteresis of 0.513% during the loading and unloading process. The voltage drift has an average of 0.24% over 20 minutes. The pinch force measurement system reveals an objective pinch force measurements in evaluating the rehabilitation progress of post-stroke patients
On the Last Iterate Convergence of Momentum Methods
SGD with Momentum (SGDM) is widely used for large scale optimization of
machine learning problems. Yet, the theoretical understanding of this algorithm
is not complete. In fact, even the most recent results require changes to the
algorithm like an averaging scheme and a projection onto a bounded domain,
which are never used in practice. Also, no lower bound is known for SGDM. In
this paper, we prove for the first time that for any constant momentum factor,
there exists a Lipschitz and convex function for which the last iterate of SGDM
suffers from an error after steps. Based
on this fact, we study a new class of (both adaptive and non-adaptive)
Follow-The-Regularized-Leader-based SGDM algorithms with \emph{increasing
momentum} and \emph{shrinking updates}. For these algorithms, we show that the
last iterate has optimal convergence for unconstrained
convex optimization problems. Further, we show that in the interpolation
setting with convex and smooth functions, our new SGDM algorithm automatically
converges at a rate of . Empirical results are shown as
well