I have just read a recent survey by

Tim Davis

Sivasankaran Rajamanickam

Wissam Sid-Lakhdar

Timothy A. Davis, Sivasankaran Rajamanickam, and Wissam Sid-Lakhdar,“A survey of direct methods for sparse linear systems (link)”. The authors state their goal in the abstract:

The goal of this survey article is to impart a working knowledge of the underlying theory and practice of sparse direct methods for solving linear systems and least-squares problems, and to provide an overview of the algorithms, data structures, and software available to solve these problems, so that the reader can both understand the methods and know how best to use them.

I have very much appreciated the breadth of the survey. It reviews the earlier work on methods for the classical problems (e.g., LU, QR, Cholesky factorizations) and gives the context of the recent work (e.g., GPU acceleration of the associated software; most recent problems of updating/downdating; exploiting low-rank approximations for efficiency).

One of the most impressive parts of the surveys are their reference lists. This one has 604 bibliographic items (if I did not do any errors in counting). There is great scholarly work in collecting 604 bibliographic items, reading through them, and putting them into a well-organized survey. There is virtually no bulk references; all citations come with at least a few words. This assiduous approach got me excited and I dug into the reference list. The earliest cited work is from 1957 (one by Berge [1], and one by Markowitz [2]); the latests are from 2015 (there are a number of them). There are no cited papers from the years 1958, 1959, 1960, 1962, 1964, and 1965. Here is a histogram of the number of papers per 5-year periods (centered at years 1955 to 2015 by increments of 5, e.g., 1955:5:2015).

The histogram tells at least two things: (i) much of the activities at the foundations of today’s methods are from the years 1990–2000; (ii) the field is very active, considering that the survey gives an overview of fundamentals, and recent developments which did not fit neatly into the grand/traditional lines of the world of direct methods are only summarized in a relatively short section (Section 12).

I underlined another quotation from the survey:

Well-designed mathematical software has long been considered a cornerstone of scholarly contributions in computational science.

This is a great survey, even for those who know the area. Kudos to Tim, Siva, and Wissam for having crafted it.

**References**

- Claude Berge, Two theorems in graph theory, Proceedings of the National Academy of Sciences of the United States of America 43(9), 842–844, 1957 (link).
- Harry M. Markowitz, The elimination form of the inverse and its application to linear programming, Management Science, 3 (3), 255–269, 1957 (link).