William F. Mitchell, a computer scientist at the National Institute of Standards and Technology’s (NIST) Applied and Computational Mathematics Division from 1993-2018, died on October 15, 2019 at age 64 after a year-long struggle with cancer. He is survived by his wife of 36 years, Becky Ross.
William F. Mitchell (1955-2019).
Born on July 25, 1955 in Oneonta, NY, Bill graduated from Clarkson University with a B.S. in mathematics in 1977. He went on to study computer science at Purdue University (M.S., 1983) and the University of Illinois at Urbana-Champaign (Ph.D., 1988). For his Ph.D., Bill studied the numerical solution of elliptic partial differential equations (PDEs). In his thesis he unified three separate hot topics of the day—high order finite element discretizations, adaptive grid refinement, and multigrid linear equation solution—into a coherent and elegant whole using a hierarchical finite element basis for approximation and newest vertex bisection of triangles for adaptivity. Bill implemented his methods in a well-crafted software package, MGGHAT (MultiGrid Galerkin Hierarchical Adaptive Triangles), which he released into the public domain. The methods implemented in MGGHAT were among the most efficient of the day. That software has since recorded more than 128,000 accesses from Netlib.
Following his studies, Bill spent five years at the General Electric Advanced Technology Laboratory in Moorestown, N.J., where he worked primarily on digital signal processing applications, one of which led to a patent on fault-tolerant Kalman filter systolic arrays. In 1993 Bill joined NIST where he worked to refactor his methods for elliptic PDEs to take advantage of increases in performance promised by emerging parallel computer architectures. This was quite challenging, since adaptive grid refinement and multigrid—the keys to sequential performance—are characterized by data access patterns that stymie straightforward parallelization. Not deterred, Bill continued to innovate, developing a novel parallel approach to multigrid (the full domain partition) and a dynamic load balancing method (the refinement-tree based partition), which proved highly effective. A new software package emerged, PHAML (Parallel Hierarchical Adaptive Multi-Level), first released in 2006. Some 2,100 downloads ensued in the very first year, and PHAML has since been used worldwide to solve challenging problems in quantum physics, fluid dynamics, heat transfer, astrophysics, and beyond, as well as in classroom settings. Bill’s code for refinement tree partitioning was also included in Sandia’s Zoltan library.
In the years following, Bill continued to refine his methods and improve his software, using it as a platform for studies in the numerical analysis of PDEs and collaborations with colleagues in the NIST Laboratories who had particularly difficult problems to solve. The former included insightful practical comparisons of the performance of a wealth of strategies for h and hp adaptive refinement. The latter included computation of eigenfunctions describing the interaction of ultra-cold neutral atoms held in an optical trap, analysis of scanning electron microscope images, and simulation of alloy solidification.
Bill took pride in his software, which was exquisitely engineered. He wrote beautiful code. He was also an expert in the modern instantiations of the Fortran programming language, advising many on its proper use, and making contributions to Fortran standards. For example, as part of his work, Bill needed to access the industry standard OpenGL graphics library, which was written in C. So, he developed an interface specification for access of OpenGL from Fortran. He implemented these in a library, f90gl, which also saw wide distribution. Bill’s interface satisfied an important need, and they were subsequently adopted by the OpenGL community as the standard Fortran bindings for OpenGL.
Bill was also quite active professionally. He was an associate editor of the Journal of Numerical Analysis, Industrial and Applied Mathematics (2006-2018) and its predecessor, Applied Numerical Analysis and Computational Mathematics (2001-2005). He was on the scientific committee of the International Conference of Numerical Analysis and Applied Mathematics (ICNAAM) from 2003 to 2018. He was a frequent participant in the SIAM Conference on Parallel Processing for Scientific Computing, the SIAM Conference on Computational Science and Engineering, and the Copper Mountain Conferences on Multigrid Methods. Over his career, he published 50 scientific papers and gave over 100 talks. In 1996 he received the Department of Commerce Bronze Medal for Superior Federal Service.
Quite a well-rounded person, Bill had many interests beyond computational science. He was an avid vegetable gardener. He was a fixture at local bowling alleys, where he competed along with NIST colleagues. He was a connoisseur of fine beers, many of which were created in his own home-brew cellar. Every year he and Becky would host an Octoberfest celebration in their backyard for their wide circle of friends featuring Bill’s beers and bratwurst created from their own recipe, all enjoyed with lively German oom-pah music playing in the background. Folk music was also a passion of Bill’s. He was an accomplished hammered dulcimer player and could often be seen playing with a local Irish ceilidh band. He and Becky were also a performing duo on the violin, known as Peat and Barley, who entertained at weddings and wineries. Peat and Barley produced several CDs of music, some of which are still available.
Bill will be fondly remembered not only for his scientific contributions, but for the joy he brought to his many friends and colleagues.