Sijmen de Jong passed away on October 30, 2010.

I first heard of Sijmen not long after finishing my dissertation. It was late 1992 or so, and I was working at Battelle, Pacific Northwest National Laboratory (PNNL). Sijmen had gotten a copy of an early version of PLS_Toolbox which was available on the internet via FTP. I received a letter from Sijmen with a number of “suggestions” as to how the toolbox might be improved. As I recall, the letter ran at least 3 pages, and included two floppy disks (5.25 inch!) filled with MATLAB .m files.

I was initially taken aback by the letter, and recall thinking, “Who is this guy?” But it didn’t take me long to figure out that, wow!, there was a lot of good stuff there. Several of the routines were incorporated into the next release of PLS_Toolbox, and modifications were made to several others. I’m sure there is still code of his in the toolbox today!

Sijmen was especially interested in the work I’d done with Larry Ricker on Continuum Regression (CR) [1], as he had just published on another continuously adjustable technique, Principal Covariates Regression (PCovR) [2]. He was also working on his SIMPLS [3] algorithm for PLS around that time. Sijmen suggested that the SIMPLS algorithm might be extended to CR. This started a collaboration which would eventually produce the paper “Canonical partial least squares and continuum power regression” in 2001 [4]. I still think that this is the best paper I’ve ever had the pleasure of being associated with. It won the Unilever R&D Vlaardingen “Author Award,” and I still display the certificate proudly on my office wall.

While CR is primarily of academic interest, SIMPLS has become perhaps the most widely used PLS regression algorithm. The reasons for this are evident from several of my recent posts concerning accuracy and speed of various algorithms. If you have done a PLS regression in PLS_Toolbox or Solo, you have benefited from Sijmen’s work!

Sijmen was the kind of smart that I always wanted to be. He seemed to see clearly through the complex math, understand how methods are related, and see how a small “trick” might greatly simplify a problem. As another colleague put it, “A very clever guy!” Beyond that, he was easy to work with and fun to be around. I regret that I got to be around him socially only a few times.

Rest in peace, Sijmen. You will be missed!

BMW

[1] B.M. Wise and N.L. Ricker, “Identification of Finite Impulse Response Models with Continuum Regression,” J. Chemometrics, 7(1), pps. 1-14, 1993.

[2] S. de Jong, H.A.L. Kiers, “Principal Covariates Regression: Part 1, Theory,” Chemo. and Intell. Lab. Sys., Vol 14, pps. 155-164, 1992.

[3] S. de Jong, “SIMPLS: an alternative approach to partial least squares regression,” Chemo. and Intell. Lab. Sys., Vol. 18, pps. 251-263, 1993.

[4] S. de Jong, B.M. Wise and N.L. Ricker, “Canonical partial least squares and continuum power regression,” J. Chemometrics, 15(1), pps. 85-100, 2001.