Lawn Bowling in Golden Gate Park

I biked to work again Thursday morning, and once again cut through the Children's Playground. But then noticed the Lawn Bowling facility just behind it. Which was an odd coincidence, b/c Arjun had e-mailed just the previous day that he wanted to check this out when we meet in the park on Sunday. So I took this pic for him.

golden gate lawn bowling
Originally uploaded by shooGu.

It's peaceful around there in the morning.

Measure spaces and measurable sets

Ina e-mailed that she was trying to understand what it means for a set to be measurable. Here was my quick writeup:

As the Wikipedia entry for Measure Theory says, "a measure is a function that assigns a number, e.g., a 'size', 'volume', or 'probability', to subsets of a given set."

Using the notation of that Wikipedia entry, which is pretty standard, the "given set" is X, the subsets are the members of a σ-algebra Σ over X, and the measure is a function μ: Σ -> [0, ∞]. So: a measure is a function μ on a σ-algebra Σ over a set X. A measure space consists of those 3 things: it's a triple (X, σ, μ).

So μ maps every Y \in Σ to a real number in [0, ∞], and μ(Y) is the "size" of Y under that measure. Then the measurable sets are just the sets in the σ-algebra Σ: all the sets that "measures."

Maybe I should contribute some of this to the Wikipedia entry...

Probability links: measure theory and sigma-algebras

Ina is taking a statistics course this fall, for which the prof recommended real analysis as a prerequisite. Turns out he's doing probability in quite a bit of detail. It must be b/c it's through the Econ dept.

So Ina asked me last night about the definition of a sigma-algebra. We were at Vesuvio at the time, so I told her I'd check my analysis texts at home. Royden has the material, but I figured it would be easier to send her some links. I e-mailed them to her, but figured I'd also post them here:

GooglePrint has a lot of material. Here is one titled Real Analysis and Probability that could be a good reference. But it seems like its aimed at readers already familiar with real analysis and probability. Probably a better option would be this: A First Look at Rigorous Probability Theory by J.S. Rosenthal.

It just occurred to me that I have Durrett's Probabilty: Theory and Examples at home as well. Another Cornell text that Amazon turned up, and which looks like it could be appropriate: A Probability Path by Sidney Resnick.

Amazon also led me to Billingsley's Probability and Measure, which I believe is a classic text, but again might be aimed for a more mathematically mature audience. It also led me to a couple more texts on stochastic processes (by Resnick and Durrett, actually) that I might need to take a look at sooner or later.

But to get started, the wikipedia entries for measure theory and sigma-algebra look pretty good.

Biked to work--finally!

Finally. I pulled the Tourmalet down off the wall and biked to work this morning. Doing my part to counteract the car culture.

It took me 1 3/4 years to finally work up the energy and daring to do it--but it turned out to be a nice, fairly leisurely ride. It helped that I was familiar with the route, from biking to soccer games in GG Park last fall: across 19th St to Valencia, up the bike lane, west on 15th St across Market, up Sanchez and Steiner into the lower Haight, west on Page into the upper Haight and into Golden Gate park. Cut through the playground, past the Carousel, came out where MLK meets Lincoln, near Kezar Stadium. From there, just two blocks up to Irving. Two sets of elevators--one up to Parnassus, the next up to our 11th floor perch. 30 mins door to door--about the same as if I take the shuttle.

Once I figure out how, I'll trace out the route on GoogleMaps. For now, I'll give you the driving directions, but it's not the same route at all--driving one goes over the 17th Street pass. On bike, I cut up north of Buena Vista, avoiding the hills.

The ride was so mellow. Sometimes i dream about SF as nearly car-free village, with the main arteries given over to buses and light rail, and the side streets for bikes.

O'Reilly's Web2MemeMap

Web2MemeMap
Originally uploaded by Tim O'Reilly.

Came across this via this TechCrunch post. Just added the TechCrunch RSS feed to my Rojo account a couple weeks ago.

AJAX for Anj

This link is for Anj.

It was #10 on this list of "Top 10 AJAX Applications" (thanks to Jason for passing that on).

I haven't checked out any of the others on that list. But I did start using another AJAX app, called NumSum. I actually started using it to do some calculations here at work. For simple spreadsheets, this is much prefereable to opening up Excel--and then keeping track of the resulting .xls files.

Web 2.0, people.

photos from 18th & Mission

Back in June I did a post titled "A walk to work", which was one of my most popular posts. (In that two people told me they read it.) I still haven't followed through on the idea of documenting the whole route photographically. But on Tuesday morning I did snap a handful of photos at the beginning of the route--the corner of 18th & Mission. Epicenter of the future gentrification of Mission Ave:

Our Mendo photos are also up. They're in a Mendocino 2005 group pool our 'keeper Todd set up. So far only our photos and the Marshburns' are in there.

But I'll post a writeup about Mendo soon, hopefully this weekend.

literary events

One thing that's been bothering me is that I go to less literary events here in SF than I did in Ann Arbor. Obviously there are obviously tons of readings happening every week, here in the city and also over in Berkeley, but I've only hit a handful the whole time we've been here. A large part of the reason is geography. It takes some time and effort to get to Opera Plaza (Clean Well-Lighted Place), or to the Haight (Booksmith), or over to Berkeley (Cody's), where the majority of readings happen. Unlike in Ann Arbor, where every reading was at Borders or Shaman Drum, both of them within two blocks of where we lived.

E.g., Dave Eggers did an event at Clean Well-Lighted Place (nice domain grab!) a couple weeks ago, but didn't make it up there for it. that is where Anj and I saw Amitav Ghosh in May, and where I saw Walter Mosley last summer.0

Anyways, the good thing is that the Commonwealth Club does a good number of literary events. Next week they've got Susanna Clarke on Monday and TC Boyle on Wednesday. I've never read anything by either--although I did receive a Boyle book as a gift once--but I think I'll go check them out. Might as well, since I paid for a Commonwealth Club membership.

Also, check out this science writing panel they've got coming up next month. Looking forward to that one.