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Accelerating gradient descent and Adam via fractional gradients

Journal Article · · Neural Networks
 [1];  [2];  [2]
  1. Korea Advanced Inst. Science and Technology (KAIST), Daejeon (Korea, Republic of); Brown University
  2. Brown Univ., Providence, RI (United States)

Here we propose a class of novel fractional-order optimization algorithms. We define a fractional-order gradient via the Caputo fractional derivatives that generalizes integer-order gradient. We refer it to as the Caputo fractional-based gradient, and develop an efficient implementation to compute it. A general class of fractional-order optimization methods is then obtained by replacing integer-order gradients with the Caputo fractional-based gradients. To give concrete algorithms, we consider gradient descent (GD) and Adam, and extend them to the Caputo fractional GD (CfGD) and the Caputo fractional Adam (CfAdam). We demonstrate the superiority of CfGD and CfAdam on several large scale optimization problems that arise from scientific machine learning applications, such as ill-conditioned least squares problem on real-world data and the training of neural networks involving non-convex objective functions. Numerical examples show that both CfGD and CfAdam result in acceleration over GD and Adam, respectively. We also derive error bounds of CfGD for quadratic functions, which further indicate that CfGD could mitigate the dependence on the condition number in the rate of convergence and results in significant acceleration over GD.

Research Organization:
Brown Univ., Providence, RI (United States)
Sponsoring Organization:
USDOE; US Army Research Office (ARO); US Air Force Office of Scientific Research (AFOSR)
Grant/Contract Number:
SC0019453
OSTI ID:
2282013
Journal Information:
Neural Networks, Journal Name: Neural Networks Vol. 161; ISSN 0893-6080
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

References (18)

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Generalization of the gradient method with fractional order gradient direction journal March 2020
Convolutional neural networks with fractional order gradient method journal September 2020
Fractional-order gradient descent learning of BP neural networks with Caputo derivative journal May 2017
An innovative fractional order LMS based on variable initial value and gradient order journal April 2017
Chemical gas sensor drift compensation using classifier ensembles journal May 2012
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Learning nonlinear operators via DeepONet based on the universal approximation theorem of operators journal March 2021
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Towards a Unified theory of Fractional and Nonlocal Vector Calculus journal October 2021

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