(Lenny, fondly known to many as Opa), died unexpectedly at the age of 86 on August 14, 2017 at his home in Princeton, NJ. Lenny was born on August 23, 1931 in Brooklyn, NY to parents Sophia Fuderman and Morris Baum (who were themselves first cousins). He married his high school sweet heart Julia Lieberman in 1953, the year he graduated Phi Beta Kappa, summa cum laude in mathematics, from Harvard University. He received a PhD in Mathematics from Harvard in 1958. He worked for a couple of years at the University of Chicago before moving to Princeton, NJ to work at the Institute for Defense Analysis - a Defense Department think tank which specialized in cryptography. Lenny's affiliation with IDA in Princeton spanned 1959 through 1978. He wrote over 100 internal papers there and is responsible for what has become the motto of IDA: "No idea is bad. A bad idea is good. A good idea is terrific." To his coworkers, he was a "renaissance man" who was exceptional at all aspects of problem solving, was dogged -- never giving up until he solved a problem, and was also a patient mentor and teacher whose influence lives on. Despite spending the bulk of his research career in a classified environment, Lenny published 11 refereed articles which have received a combined 9000 citations and continue to be cited to this day. Lenny's public scientific legacy includes the Baum- Welch algorithm, and co-au- thorship of the first proof, published in 1967, of its mathematical underpinnings. This algorithm directly enabled the first effective speech recognition systems. Today, 50 years later, this work remains at the center of these systems - while its mathematical and algorithmic descendants and other relatives, have impacted many fields from genomics to weather prediction to finance. After leaving IDA, Lenny teamed up with Jim Simons to apply his mathematical modeling to the financial markets. He retired early, legally blind, seeing with only his rods, having lost all his cones to a dystrophy, but that didn't stop him from travelling the world over, visiting many exotic places. He continued to trade for himself very successfully, often taking very contrarian positions. An avid Go player, deep lover of science and seeker of truth, he continued working on math literally up until his death, spending the night before he died reading new math papers on prime numbers. Like his father before him, he was a great walker, walking four miles a day up until his last few months. He was a loving husband, father and devoted grandfather. The grandchildren loved his "Opa Stories". Lenny was generous of spirit, deeply ethical, and always kind. In addition to his devotion to family, Lenny, and his late wife Julia, made his friends feel like family. He will be deeply missed by the many who were touched by his life, including his companion of the last decade, Maxine Lampert, with whom he shared many adventures. Lenny is survived by his two children - Eric Burton Baum currently living in Princeton, NJ, (spouse Chaitra Keshav Baum) and Stefi Alison Baum currently living in Winnipeg, MB (spouse Christopher O'Dea). Lenny is also survived by eight grandchildren: Eric's children (Nathan, Noah, Julia, and Asha) and Stefi's children (Connor, Kieran, Brennan, and Annelies). He was predeceased by the love of his life, Julia Lieberman (February 22, 1999). The funeral was held August 15, 2017, graveside at 12:00 noon at Princeton Cemetery, followed by Shiva.
Published in New York Times on Aug. 18, 2017.