13 April 2016

Rando

John D. Cook alerts us to a pitfall in seeding a random number generator (RNG) for multiple processes/threads (for instance, for a Monte Carlo simulation):
Applying the analog of the birthday problem to the RNG seeds explains why the project was launching processes with the same seed. Suppose you seed each process with an unsigned 16-bit integer. That means there are 65,536 possible seeds. Now suppose you launch 1,000 processes. With 65 times as many possible seeds as processes, surely every process should get its own seed, right? Not at all. There’s a 99.95% chance that two processes will have the same seed.

28 February 2016

Personal, in a cabinet

John Markoff has the obit for Wesley A. Clark, designe of an early computer with which I was otherwise unfamiliar. At MIT's Lincoln Laboratory in the early 1960s, an era dominated by mainframe computing, Clark built LINC, a workstation set up to fit into a medical research lab, powered by a 12-bit processor running at 0.5 MHz. As such, Clark paved the runway for personal computing and the innovative Alto by Alan Kay in the following decade.

15 February 2016

Don't stop

For businessmen and the general public, a 1928 guide to using the telegraph service effectively.

Most of us are familiar with/remember using Western Union to send money by wire, or using FTD to deliver flowers remotely. In its heyday, the telegraph system was used for sending just about anything to a distant city.

In addition to the regular money order service, the telegraph companies maintain what is known as a telegraphic shopping service. As now organized, this service permits of the purchase by telegraph of any standardized article from a locomotive to a paper or pins.

There was even an early 20th-century analog of DNS:

In the case of domestic telegrams the address and signature is transmitted free of charge, the only part of the message paid for being the body. In the case of cablegrams and radiograms, however, all words are charged for, including address and signature, with the exception that the name of the country of destination is transmitted free. In the interest of economy to the customer, cable companies permit the registering of a code address, so that it is unnecessary to transmit long addresses. Thus a message addressed "WUTRAVBURO LONDON," would be delivered to The Western Union Travelers' Bureau, 22 Great Winchester Street, London, England. There is a nominal annual charge for this registration privilege, the amount being so small as to be more than offset by the saving on a few cablegrams or radiograms.

kottke.org

01 February 2016

Upcoming

A documentary on the Antikythera Mechanism (long-time readers will recognize this as one of my hobbyhorses) is screening weekly at the National Gallery of Art through mid-March.

Imbrications

Jane Cotler and Evan Sandhaus describe two neat tricks that the New York Times used to bring a recent 20-year block of articles into its TimesMachine service. First, an image tiling and rendering procedure that minimizes download requirements. Even more interesting, a fuzzy-logic string-matching algorithm that lines up a batch of texts taken from OCR with their counterparts from a digital archive. The trick to reducing the search space depends on dividing each text into blocks of overlapping tokens called shingles, a/k/a n-grams.