## Friday, May 1

### Maths

I'm with Eric, arriving in Boston yesterday afternoon and arrive in time to see him in the classroom. He teaches a group of continuing ed students differential equations and here, he performs a simple integration using terminal velocity to provide context for introducing separation of variables. Eric is a natural. His students clearly love him - and it is a joy to see him move around the chalk board. I do note that Eric, not a slave to fashion, brings his own unique style to Harvard - he notes "homeless chic" which might not be too far off; at least it is consistent with the grunge look I see around me otherwise on campus. I am reminded how extraordinary the Harvard community - I overhear conversations in French, Arabic (I think) and Japanese while picking up on young peoples conversation (jet lag makes my senses hyper-sensitive). A group of students discuss abortion; hippies Obama. Forums cover Israel and the Middle East and market-regulation post recession where I recognise the speakers, if by name only. Extension classes offer everything to anyone who has the time and inclination. Spring campus at its best preparing for graduation and alum who, presumably, are potential doners - Harvard has the largest endowment of any school at >\$40 billion, though who knows what it is today. (Eric now paces to get at his computer)

Eric: "the most basic type of integral equation is a
Fredholm equation of the first type:

$f(x) = \int_a^b K(x,t)\,\varphi(t)\,dt.$

The notation follows Arfken. Here φ is an unknown function, f is a known function, and K is another known function of two variables, often called the kernal function. Note that the limits of integration are constant; this is what characterizes a Fredholm equation."