NCON: A tensor network contractor for MATLAB

Abstract

A fundamental process in the implementation of any numerical tensor network algorithm is that of contracting a tensor network. In this process, a network made up of multiple tensors connected by summed indices is reduced to a single tensor or a number by evaluating the index sums. This article presents a MATLAB function ncon(), or "Network CONtractor", which accepts as its input a tensor network and a contraction sequence describing how this network may be reduced to a single tensor or number. As its output it returns that single tensor or number. The function ncon() may be obtained by downloading the source of this preprint.

7 pages, 3 figures, RevTeX 4.1. Contains downloadable software v1.01. Amended download instructions to note that when clicking to download the source in .tar.gz format, arXiv actually supplies it in uncompressed .tar format. Substantial text overlap with arXiv:1310.8023: We use many of the same examples to describe the operation of ncon() as we do for the complementary package multienv()

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