Tuesday, November 12, 2019

Tribute to Godfried Toussaint by his former PhD student, Binhai Zhu

It was a shock when a colleague told me Godfried's sudden passed away.
I was Godfried's first Chinese PhD student. My story with Godfried was
sort of a drama, even though I never collaborated with him again after
my graduation in 1994. What happened during my stay at McGill
(Sep, 1991-June, 1994), especially in late 1991, changed my life completely,
both academically and socially.

I was admitted to the PhD programs at both McGill and Dartmouth in 1991.
I turned down McGill and went to Dartmouth initially. Being used to big cities
like Beijing and Toronto, I was not able then to deal with a 7000-people small
town (Hanover, NH) and felt bored and restless (it was a very small PhD program
then at Dartmouth). Arriving at Hanover in early September and after a few days,
over a boring Thursday afternoon, I dialed his number using a coin-operated
payphone in the graduate activity room --- such a vivid scene even today! I
didn't remember what I exactly complained but I still remembered his commanding
voice "Binhai, the semester already started, come back immediately!". I packed
my stuff and drove back to Montreal over the weekend.

In the early 1990s, at McGill all the PhD students had two chances to take and
pass a tough qualifier exam. Being a graduate student with some research
experience already, I wanted to start my research immediately even though I had
to prepare for the qualifier exam at the same time. I tried to select some
topics for my thesis research, but failed a few times, each after some intensive
bibliography reading. One day in the middle of October, seeing his office door
open, I knocked softly. Godfried raised his eyes and asked me how everything
was going. I told him about my puzzled feeling of being unable to find a
research topic. He replied "I remember Micha Sharir had a paper on terrains a
few years ago, and I felt there was something there!". Without any waiting, I
went to the McGill library, searched the database (no internet web browser
then!), read and photocopied Sharir's 1988 IPL paper on the third floor. By
the time I walked out of the library, in less than an hour after talking to
him, I already had an idea to slice off a log factor over Sharir's
bound --- this was the basis of my PhD thesis and the O(n log n) time algorithm
for the shortest watchtower problem is still the best today in 2019!

Godfried was sharp on identifying new research problems, so far one of the two
best people I have ever collaborated in that aspect. Teaching in a classroom,
he would sometimes suddenly stop and ask "Why must we study this problem? Could
we have a different problem?". And in several occasions this triggered his 
graduate students to research on these new problems, an example being the
'Unoriented Theta-Maxima' paper later published in SIAM J. Computing, initially
triggered by his classroom question "Why we have to restrict the maxima to be
rectilinear?". One of his casual but cutting edge opinions, "Finding problems
is sometimes more important than solving a problem.", deeply changed my way of
doing research, especially when I myself started to supervise PhD students
(some in areas out of geometry).

I left McGill in 1994 and after that I never collaborated with Godfried again,
partly due to my shift from computational geometry (though I never really gave
it up). But Godfried was always with me in different ways. We met irregularly
at conferences since 1994, and we lastly exchanged emails in 2017 about
finding a chance for me to give a talk on computational genomics in Abu Dhabi
(so that we can meet again!). This is not to happen. On the other hand,
maybe this is not really a pity as some part of Godfried, his mind, thoughts
and more, will be around in this world for a long long time, and I can feel it!

Godfried, you will be deeply missed!