Towards an Efficient Use of the BLAS Library for Multilinear Tensor Contractions

TL;DR

This paper investigates how to efficiently perform tensor contractions using the BLAS library, specifically identifying when GEMM can be applied and providing guidelines for optimal use based on tensor properties.

Contribution

It establishes conditions for using GEMM in tensor contractions and offers a classification and practical guidelines to improve computational efficiency.

Findings

Conditions for applying GEMM to tensor contractions are defined.

A classification of tensor contractions into three groups is proposed.

Guidelines for effective use of BLAS in tensor computations are provided.

Abstract

Mathematical operators whose transformation rules constitute the building blocks of a multi-linear algebra are widely used in physics and engineering applications where they are very often represented as tensors. In the last century, thanks to the advances in tensor calculus, it was possible to uncover new research fields and make remarkable progress in the existing ones, from electromagnetism to the dynamics of fluids and from the mechanics of rigid bodies to quantum mechanics of many atoms. By now, the formal mathematical and geometrical properties of tensors are well defined and understood; conversely, in the context of scientific and high-performance computing, many tensor- related problems are still open. In this paper, we address the problem of efficiently computing contractions among two tensors of arbitrary dimension by using kernels from the highly optimized BLAS library. In particular, we establish precise conditions to determine if and when GEMM, the kernel for matrix products, can be used. Such conditions take into consideration both the nature of the operation and the storage scheme of the tensors, and induce a classification of the contractions into three groups. For each group, we provide a recipe to guide the users towards the most effective use of BLAS.