from Erik Winfree

Like for so many of the people posting here, Sam was an inspiration to me. Someone who knew what it meant to be a good person - in heart and in mind - and had the will to do it. I miss him so much.

I met Sam in graduate school, when we were both in John Hopfield's group. It was an amazing time. We were all young, learning what it was to be a scientist. Sam delighted in the process, and delighted in reminding people of the joy of having so much to learn. In my mind, I can still hear him saying, "Ah, young butterfly, haven't you heard that the trace of the matrix is the sum of the eigenvalues? Let me show you why..."

He took such joy in seeing people understand - in seeing people happy, for whatever reason. He loved sharing intellectual jewels the way some people love telling jokes. We'd seldom see each other without his telling me about the latest mind-bogglingly beautiful result that he was enamored of. Maybe this week it's Propp & Wilson's exact sampling from markov chains, with applications to tilings, explained enchantingly in terms of a time machine and living backwards. And if I was too slow to catch the explanation in real time (I usually was) then it wouldn't be long before I'd get an email from Sam, spelling it all out in detail.

Sam loved sharing himself to make people happy. He was a people person. I had never heard of the phrase, "people person", before I met Sam - and if I had, I wouldn't have thought that a people person could also be a deep intellectual. Doesn't deep understanding entail privation and solitude and a retreat from the softer emotions? But knowing Sam disabused me of that conceit.

He was also perfectly willing to demand something of people - if the demand came with caring and love. Like the demand to take care of the world. Another concept Sam introduced me to was dumpster diving. But not dumpster diving as a cheap way to fill your fridge with perfectly good food the supermarkets were throwing away. Rather, it was clear he was talking about dumpster diving as social activism in protest of our society's wasteful ways. That, and the cup hanging by a carabiner from his enormous backpack.

I don't know if I've met anyone else who had the goodness of humanity so deeply embedded in his heart.

We'd have discussions about the future of society in the wee hours of the morning. Sam wasn't afraid to see that our world is changing, and that we should prepare for it - no: that we should take a role in guiding it for the better. I remember talking about the ever-increasing presence of surveillance cameras and email snooping and Big Brother and how it scared me, and Sam countering by explaining why he strived to live a life of openness with no secrets and no shame, because he saw the only solution being to prevent the government from being the ONLY ones with such pervasive knowledge; everyone must have access to the same information, so we must learn to live wisely in a world with no secrets and no privacy. That made me think, for a long time. I was surprised by his conclusion, and also surprised by his confidence that he could live a life so clean, so pure, that with no privacy would come no shame. I think he always strived for that kind of purity of feeling.

Many of my memories about Sam come from our time working together in the early days of DNA computing. When Paul Rothemund and I came back from the first conference on DNA-based Computers flushed with excitement, Sam joined us in the adventure and soon the three of us were meeting every week or so with Len Adleman and his friends at USC. We would have wide-ranging talks about life and science on our long drives to and from Len's lab or home. Sam was irrepressible, stripping our ideas down to their simplest and cleanest essence, suggesting new possibilities and new ways of looking at things, breaking our mental roadblocks with his insistence to understand: "Why?" and "Why not?" And always he would urge us on with his enthusiasm, or buoy us up with wise words when we were discouraged, overwhelmed, or depressed. (I sure could use a dose of Sam right now.)

To Sam, science was personal. So anyone could do it. With whatever was handy. Of such spirits was born the Sunday Experiment Club, with the charter to think about and do something unrelated to our thesis research every weekend. Alas, we only met twice - but the inspiration remains, as do memories of trying to move fluorescent DNA around in a puddle of saltwater by means of a 9V battery and two electrodes.

Of course, we all know that DNA computing wasn't Sam's destiny and it wasn't his true passion. I guess it was a hobby - a chance to drink more broadly of the scientific experience. And also sometimes I wonder if he did it just to be with his friends, us... maybe it was as much fun for him as stealing a city transit bus for a scavenger hunt? I don't know how he managed to squeeze it all in between writing "EM algorithms for PCA and SPCA" and "A unifying review of linear gaussian models". Sometimes I felt guilty that our collaboration took so much of his time away from his true passion. Perhaps more surprising is that at times it seemed that only his friends could see that machine learning was his true passion, and we had to convince him not to give up on it when he was afraid he would have nothing great to contribute.

One wants to remember Sam as a shooting star, blazing through the night sky with inspiring purpose and direction. But it wasn't always so. Like any mortal, at times Sam grappled with finding meaning and direction in his life. He seriously wanted to be an astronaut, for example, and was torn by the thought that being an expert in machine learning was not a ticket to the sky. What I admired so much about him, though, was how he never stopped thinking about what life meant, what principles to live for, how to do right by others - whether or not he knew any answers. He was a serious and sincere person in the most fun-loving way.

Sam loved to entertain us with stories, too. He had a lot of them, each delightful. Here's one, as best I remember it: Halloween. Sam's a young kid. Dad wants to make him a real special costume. 1 raincoat. 1 umbrella. 1 leaky "cloud" on a stick. Attach above umbrella. 1 basin for collecting water. Install around legs. 1 water pump, battery powered. Place in backpack, route tubing from basin to cloud. And little Sam walks from house to house with a rain cloud over his head! What fun!

P.S. For the geeks out there, I'll include one of Sam's signature files from grad school days.