# 9 November 2018

Today was a great day at the school. There were two remarkable events. The first one is the 30th anniversary of the lab LIP at ENS Lyon (here is the program). The second was that the ENS Lyon awarded Marc Snir with an honorary doctorate degree (Docteur Honoris Causa). The page announcing this event is in French and google translate does a good job in translating it to English. Yves Robert had slides for introducing Marc during the event.

Many of us know Marc (ever heard of the MPI standard and the book “MPI: The complete reference“). His work span complexity theory, to MPI standard, to parallel computing systems. And oh, he speaks French.

I was lucky to see his talk during the 30th anniversary of the LIP (but unlucky to miss the ceremony of Docteur Honoris Causa). He gave an overview of his involvement with building parallel machines: BlueGene, Blue Waters, SP/Vulcan, and others. His talk has many whimsical observations. Here are some:

• A supercomputer research prototype is an oxymoron.
• A supercomputer research design is either boring or unpractical.
• The main contribution [of all the supercomputer design projects]: The projects educated a generation of researchers.
• Theory informs practice, but should not be taken literally.

After stating

Often theory follows practice, rather than practice following theory

he discussed how his paper with Upfal and Felperin was motivated by Vulcan’s practically well behaving design of $\log N + O(1)$ stages. Back then, the theory demonstrated $2\log N$ stages to avoid worst cases. The cited paper shows $\log N + \log\log N$, where the extra term is $O(1)$ for practical purposes.

After the talk, I wondered which computer he helped to build was his favorite. He said, more or less,

I created them, so all are my favorite !

### References

Eli Upfal, Sergio Felperin, and Marc Snir, Randomized routing with shorter paths, IEEE Transactions on Parallel and Distributed Systems, 7(4), pp. 356–362, 1996. (doi)