Abstract

This paper provides a unified description of Widening, a framework for the use of parallel (or otherwise abundant) computational resources to improve model quality. We discuss different theoretical approaches to Widening with and without consideration of diversity. We then soften some of the underlying constraints so that Widening can be implemented in real world algorithms. We summarize earlier experimental results demonstrating the potential impact as well as promising implementation strategies before concluding with a survey of related work.

Highlights

  • In particular we make the distinction between explicit partitions of the model space and how partitions can be closed under refinement or just weakly closed when the selection operator has been applied as well

  • Afterwards we introduced the notion of path-based Widening which relies on the selection operator to implicitly segment the model space

  • We discuss an aggregate of earlier results, highlighting potential pitfalls and providing an intuition for different approaches to realize Widening in practice

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Summary

Motivation and introduction

The trend to add more cores to modern processors and the growing popularity of cloud based compute resources has increased the importance of parallel algorithm development. Instead our goal is to improve model quality without increasing the overall time spent by investing parallel resources into better exploration of the (model) search space These types of search problems are widespread in machine learning and data mining with models relying on numerical parameters that need optimization, discrete models turning this into a combinatorial search problem, and sometimes a hybrid of both. We provide a formalization of Widening combining, expanding, and unifying earlier publications (Akbar et al 2012; Ivanova and Berthold 2013) that describe a number of ideal methods for Widening of this type of search and reducing the impact of the greedy heuristic These choices differ in how they widen the search with various partitioning methods.

Preliminaries
Selection and refinement
Widening
Top-k widening
Ideal partitioning for widening
Approximate partitioning for widening
Path-based widening
Diversity-driven widening
Ideal diversity-driven widening
Randomized diversity-driven widening
Summary
Practical considerations and experimental insights
Injecting diversity
Explicit diversity: diverse top-k
Explicit diversity: data- versus model-driven diverse top-k
Implicit diversity
Implicit diversity: hashed bucket selector
Experimental insights
Runtime observations
Lessons learned
Related work
Machine learning algorithm parallelization
Speed-up through parallelization
Specific frameworks
Model quality improvement
Look ahead strategies
Ensemble learning
Meta heuristics
Monte Carlo tree search
Federated learning
Greedy search algorithm improvement
Parallel local search
Communication reduction
Findings
Full Text
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