Tea Total

Moving

2005-11-15T20:41:00.000-08:00

I'm moving to a new bat place and new bat format: Numerical Notes. This move is spurred by a combination of technical and personal considerations. On the technical side: I mostly spend my evenings away from computer networks, which means that the times I'm most likely to take a break and blog are also the times that I'm least likely to have the connectivity to post anything. Also

Understanding and reviewing

2005-10-04T20:02:00.000-07:00

In How to Solve It, Polya lists four steps for mathematical problem-solving: understand the problem, devise a plan, carry out the plan, and then look back. It seems like I spend most of my time -- or at least most of my interesting time -- in the understand the problem or the look back phases. In some sense, I spend way more time in the phases of initial understanding and later

Another week in books

2005-10-03T15:13:00.000-07:00

Adventures of a Mathematician (S. Ulam) Did I finish this two weeks ago? In any case, it was interesting to read. In addition to the autobiographical and historical comments, Ulam says a great deal about mathematics and mathematical ways of thinking. Though he sometimes mentions specific technical areas, almost all of the book is accessible to a general audience.

Windows woes

2005-10-02T12:06:00.000-07:00

I wish I had a better idea how to effectively use a Windows box at a distance. Now that my old laptop is retired, I no longer have such easy access to a Windows machine. The department has a server that I can use with rdesktop, but it's of limited usefulness: I can't run MATLAB on it to compile my codes; I can't print from it; and for security reasons, I can't access it from the

Frequently searched questions

2005-09-28T18:44:00.000-07:00

The word you're thinking of is teetotal. It's an adjective that describes one who does not drink. It is a pun, since I prefer tea to alcohol (though I've decided a cup of cider from time to time is okay, too). There are two aspects of MATLAB EXternal interface (MEX) programming that cause most of your headaches. First: when you use the mex script, the compiler

Time out for reading

2005-09-19T10:36:00.000-07:00

Time out for reading There is a new Half Price books in Berkeley, along Shattuck Avenue a couple blocks west of campus. Curiously, they're in the same space as the dollar store where I got some pans and utensils just after I moved to Berkeley. As part of their opening celebration, they have an additional 20% off. So I wandered in, saw some familiar faces, and picked up a few

Multiples of q

2005-09-19T10:35:00.000-07:00

You probably learned this trick in grade school: to see whether a number is divisible by three, add all the digits and check if the sum is divisible by three. The same thing works for nine. Ever wonder why? Actually, three and nine are just special cases of something very general. What does it mean if q divides n evenly? It means that there is ultimately no remainder in the

Penguins

2005-09-16T11:15:00.000-07:00

A friend pointed out this, which I think is one of the most entertaining uses of GIF animation that I've seen in a long time.

A little long division

2005-09-12T09:54:00.000-07:00

Suppose p and q are relatively prime integers, and 0 < p < q. If q has any prime factors besides 2 and 5, then a decimal expansion of p/q will eventually start to repeat. How long will the repeating part be? Looking at the sequence of digits is actually a very difficult way to approach this problem. It's much simpler to look at the sequence of remainders. Remember how long division works.

Honest exercise

2005-09-06T17:01:00.000-07:00

Alas, we didn't get through all the Common Lisp exercises I'd planned for section today. This is too bad, because I would have liked to have people think about the last exercise: given a collection of (programmer program) pairs, how can you find the sets of programmers with structurally identical codes? It took me about five minutes to do this one (though this may be because I

Law and linear algebra

2005-09-05T11:34:00.000-07:00

The Economist has an article on using linear algebra network analysis tools to identify important legal cases. This is the same technology used by some search engines to find important web sites (hubs and authorities). I learned about this from a posted on NA digest. Currently drinking: Coffee

Cycling for digits

2005-09-05T10:49:00.000-07:00

There's a computer language called Nickle which grew out of something Keith Packard started working on two decades ago because he needed to do a little arbitrary-precision calculation. One of the entertaining features of the language, particularly if you're trying to teach people about compilers, is the treatment of rational numbers. Every rational number can be written as a

On the radio

2005-09-03T13:44:00.000-07:00

The AC voltage provided by the local power company is a bit over 60 Hz. Consequently, most of the clocks in the house (excepting the battery-powered ones) end up running fast. They all got reset to the correct time when daylight savings started; now they're about fifteen minutes out of sync. Consequently, my alarm goes off at 7:15, now, even though the clock thinks it's 7:30. I

Fall 05

2005-08-25T17:41:00.000-07:00

Classes start next week. How about that? A couple years ago, I was the TA for the local graduate parallel computing course. That was a lot of fun, though it was also a lot of work. Kathy Yelick has done a lot with performance tuning and language design for parallel machines; and I'm a numerical analyst who happens to know something about systems. So I think the folks taking the

Local names

2005-08-24T16:08:00.000-07:00

Modern programming languages support the notion of restricted lexical scope: the meaning assigned to a name can be made to hold only over restricted sections of the program text, allowing the programmer to re-use the same symbol to refer to different things depending on the context. It's hard to overstate how useful this is. It's so useful, in fact, that we fake it when we don't have

Essays interspersed

2005-08-23T09:21:00.000-07:00

Richard Gabriel, Paul Graham, and Peter Norvig all have sites of essays. Norvig has more technical stuff than Graham or Gabriel, but all three collections are worth browsing. I've already mentioned Graham's essays, but if you're unfamiliar with the other two: Norvig is Director of Search Quality at Google, but I know him better as the author of The AI Book (together with

Day in the life

2005-08-16T16:01:00.000-07:00

Get up. Coffee. Tease flatmate. Taylor's theorem, integration by parts, Cauchy-Schwartz. Rinse and repeat. Get error estimate. Check numerically whether estimate holds for simple test case. Discover algebra errors in the proof. Correct proof. Discover algebra errors in the test program. Correct test program. Discover errors in the compiler. Swear. Let out cat, who is

Starts with P

2005-08-14T13:59:00.000-07:00

Public transportation I visit Winnie in San Jose most Saturdays. The full trip proceeds in three legs: a BART ride to Fremont, a bus ride to a transfer station at the Great Mall transit center, and a light rail ride to a stop near Winnie's apartment. Depending on how long I spend waiting between each leg (and whether I meet Winnie at her apartment or at Great Mall), the trip

Messiness and computing

2005-08-12T12:25:00.001-07:00

Heidi recently wrote an entry in praise of messiness in science, which set me thinking about messiness in mathematics and in computing. While reading some of Dijkstra's old writings, I came across this tidbit, which seemed apropos: We should never forget that programmers live in a world of artifacts, a fact that distinguishes them from most other scientists. A programmer

Three books

2005-08-12T12:25:00.000-07:00

The Structure of Scientific Revolutions. Thomas Kuhn You've heard of this book, even if you don't think you have. Kuhn gave the modern meaning to the phrase paradigm shift. You may recall that I mentioned this book -- a month ago, perhaps? It took me a while to read it, just as it took me a while to read it the first time I was exposed to it some ten years ago. I tried

Backstroke of West

2005-08-11T13:46:00.000-07:00

There's an old story about the phrase the spirit is strong, but the flesh is weak being translated to Russian and back to English to yield the vodka is good, but the meat is rotten. I thought that was funny. I nearly hurt myself reading about this English-subtitled Chinese edition of Revenge of the Sith. Back to Sobolev estimates.

Little things

2005-08-09T15:15:00.000-07:00

I like pen and ink drawings, the kind in which every line is critical to the picture. I enjoy short poems, sonnets, and lyrics in which each sound and connotation is placed just so. I appreciate Strunk and White, Kernighan and Ritchie, and Rudin. I love ripe summer tomatoes with naught but a sprinkle of salt. Romantic landscape paintings, Wagner's Ring Cycle, Gibbon's history,

Search terms 2

2005-08-05T16:03:00.000-07:00

Searching for Lisp tokenizer or Lisp parser -- nearly useless. Searching for Lisp regular expression -- much more useful. Google -- priceless.

Macro expanding disclaimers

2005-08-05T15:14:00.000-07:00

From the CLiki Common Lisp resource site: Imagine a fearsomely comprehensive disclaimer of liability. Now fear, comprehensively.

Linear B

2005-08-03T17:50:00.000-07:00

I gave my advisor an early draft of my thesis early in May; he returned the marked up version to me a couple weeks ago. There was a section in my draft which I cut from previous documentation of one of my codes in which I described the mixed-language structure of the code as a combination of C++, Fortran, Lua, MATLAB, and Minoan linear B script. I forgot to cut the last one from