tag:blogger.com,1999:blog-52801912023-11-15T05:51:08.687-08:00Tea TotalA cup of tea, a cat, a book, and a pile of scrap paper. What more does one need?Unknownnoreply@blogger.comBlogger509125tag:blogger.com,1999:blog-5280191.post-1132117014781848882005-11-15T20:41:00.000-08:002005-11-15T20:56:54.793-08:00Moving
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. AlsoUnknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1128486740570460872005-10-04T20:02:00.000-07:002005-10-04T21:32:20.620-07:00Understanding and reviewing
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 laterUnknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1128377633654984832005-10-03T15:13:00.000-07:002005-10-03T15:14:03.066-07:00Another week in books
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.
Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1128280040564654272005-10-02T12:06:00.000-07:002005-10-02T12:07:20.573-07:00Windows woes
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 Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1127960576418645222005-09-28T18:44:00.000-07:002005-09-28T19:22:56.426-07:00Frequently searched questions
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 Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1127151409017456492005-09-19T10:36:00.000-07:002005-09-19T10:36:49.023-07:00Time out for readingTime 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
Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1127151373838686122005-09-19T10:35:00.000-07:002005-09-19T10:36:13.846-07:00Multiples of q
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 Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1126894708735144482005-09-16T11:15:00.000-07:002005-09-16T11:18:28.740-07:00Penguins
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.
Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1126544150942931412005-09-12T09:54:00.000-07:002005-09-12T09:55:51.010-07:00A little long division
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.Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1126053435660102412005-09-06T17:01:00.000-07:002005-09-06T17:37:15.666-07:00Honest exercise
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 Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1125945565285962122005-09-05T11:34:00.000-07:002005-09-05T11:39:25.290-07:00Law and linear algebra
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
Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1125942592224720532005-09-05T10:49:00.000-07:002005-09-05T10:49:52.233-07:00Cycling for digits
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 Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1125781908500035572005-09-03T13:44:00.000-07:002005-09-03T14:11:48.506-07:00On the radio
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 Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1125022124630750322005-08-25T17:41:00.000-07:002005-08-25T19:08:44.653-07:00Fall 05
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 theUnknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1124927749184330942005-08-24T16:08:00.000-07:002005-08-24T16:55:49.193-07:00Local names
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 haveUnknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1124818916767686002005-08-23T09:21:00.000-07:002005-08-23T10:41:56.813-07:00Essays interspersed
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 Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1124233353962601672005-08-16T16:01:00.000-07:002005-08-16T16:02:33.966-07:00Day in the life
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 isUnknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1124053169255548612005-08-14T13:59:00.000-07:002005-08-14T13:59:29.266-07:00Starts with P
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 Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1123875355721583692005-08-12T12:25:00.001-07:002005-08-12T12:41:35.510-07:00Messiness and computing
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
Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1123874731688446802005-08-12T12:25:00.000-07:002005-08-12T12:41:11.793-07:00Three books
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 Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1123793320554164512005-08-11T13:46:00.000-07:002005-08-11T13:48:40.560-07:00Backstroke of West
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.
Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1123625858872947562005-08-09T15:15:00.000-07:002005-08-09T15:17:38.876-07:00Little things
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,
Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1123283046245107992005-08-05T16:03:00.000-07:002005-08-05T16:04:06.250-07:00Search terms 2
Searching for Lisp tokenizer or Lisp parser -- nearly useless.
Searching for Lisp regular expression -- much more useful.
Google -- priceless.
Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1123280211673158892005-08-05T15:14:00.000-07:002005-08-05T15:16:51.680-07:00Macro expanding disclaimers
From the CLiki Common Lisp resource site:
Imagine a fearsomely comprehensive disclaimer of liability. Now fear,
comprehensively.
Unknownnoreply@blogger.comtag:blogger.com,1999:blog-5280191.post-1123117070287505342005-08-03T17:50:00.000-07:002005-08-03T17:57:50.293-07:00Linear B
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
Unknownnoreply@blogger.com