Lyapunov equation on 2-jet [Byzantine]

Reminding myself that I jotted down the following sequence of steps back in May:

  1. Write the partial differential equations for a Lyapunov function v as an exterior differential system in the 1-jet of v, using the contact form.
  2. Write the equation in the 2-jet of v.
  3. Then write it again in the 2-jet, using the connection forms, to bring in the Riemannian geometry of the manifold.
  4. Now write the partial differential equation of Kalman filtering in the 2-jet of the total space.
  5. Repeat using the connection forms.

In the last month or two I have made very little progress beyond step 2. This is not encouraging. Progress on solving a partial differential equation that defines a common Lyapunov function for two vector fields a and b was also limited.

Espanha na Copa do Mundo

A Espanha parece que está com um timaço na Copa das Confederações. Meu palpite é que nunca vai ser campeã mundial sem uma escola nacional. A Catalunha poderia ser campeã mundial, os castelhanos talvez, ou até o País Basco. A Espanha pode ganhar essa mini-Copa na África; ganhar a Copa do Mundo, duvido.

Hezbollahi, lá e aqui

Segundo um colega, os sindicatos da Usp não se pronunciam sobre política internacional. Agora é uma boa ocasião para lembrar que eles abriram exceção para apoiar o Hezbollah em 2006, como se pode ver nas páginas da Adusp e do Sintusp. Segundo eles ” … O Hizbollah surgiu … da resistência popular espontânea….. é responsável pelos programas sociais….” Esses hezbollahi são os mesmos que estão matando meninas nas ruas de Tehran. Que Tutatis nos livre da extrema direita, da assim-chamada esquerda que os apoia, e dos “programas sociais” deles.

Quiet playground

Brookline is a small town of many, many parks. I had imagined we knew most of them, but on my way to the Boston University library I saw a small playground we had never used. Rosa and Hannah have probably outgrown its unusual, small structures. The quiet and shady place filled me with saudades.

Academic genealogy [byzantine]

Since I last looked at it, the Mathematics Genealogy Project has added a fair amount of interesting information. I had not been aware, for instance, that Norbert Wiener is my great-great academic grandfather – his student’s student was my advisor’s advisor. Wiener’s doctoral work was in philosophy, so through him my work is related to a long line of continental thought. The link to Kant himself is a little forced – not all the contributions in the site follow the highest standards of academic precision – and in any case the connection does not get me excited about continental philosophers. The imaginative reader may try to imagine a Freudian interpretation of my efforts to put some sense into non-stochastic estimation in non-Euclidean spaces.

More interesting is the link to a long line of scholars down to the Italian Renaissance and earlier, which appears to be shared by an overwhelming majority of contemporary scientists. The earliest person on the database was Georgios Gemistos Plethon, and without attempting to check all the intermediate links, I managed to add one more generation by finding about his late Byzantine Empire “advisers” in the book “Byzantine philosophy and its ancient sources,” by Katerina Ierodiakonou (Oxford; New York: Clarendon Press, 2002).

The relevant part about Plethon’s advisor Elissaeus, sometimes also called Judaeus, is in the chapter by Polymnia Athanassiadi, pages 248 to 250. George Gemistos (Plethon) had as tutor Demetrios Kydones, a pupil of Nicholas Kabasilas (thinking carefully, I would not use the word adviser to characterize their relationship – teacher would be better). As a young man Gemistos traveled to Adrianople (Turkish Edirne) to study with Elissaeus Judaeus, a mysterious figure who may or may not have been a Jew despite the epithet, but apparently managed to get himself burned at the stake anyhow. Gemistos studied with Elissaeus as a live-in pupil, in a relationship that I judge can be appropriately called advisor-advisee. Much later in his life he wrote Nomoi (“Book of Laws”), but it is clear that this work was based on his studies of Zoroastrianism with Elissaeus. I judge that it can properly be called his thesis advised by Elissaeus. As such it was considered by Gennadios Scholarios, the first Ottoman Patriarch of Constantinople, who burned most of the book after Plethon’s death. I find it hard to give a date for the thesis, though the advisor-advisee relationship probably happened in the 1380s.

Though we would not recognize his line of work as that of a mathematician, Plethon did some astronomical calculations besides his now better-known philosophical work. He was highly regarded in Florentine Renaissance for his knowledge of Plato and ancient Greek philosophy, and as such occupies a rightful place in our mathematical genealogy. It would be interesting to extend the genealogical investigation down to the original Greeks, but I suspect that the Byzantine early Dark Ages will prove unsurmountable.

O blog da Dilma é um horror

O blog da Dilma é um horror! Estridente, pouco presidencial. Mal escrito, em linguagem vulgar. Ela até tem qualidades, mas se fizer campanha for como faz blog, não chega lá. Se chegar, vamos ter muita saudade do Lula.