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[quote=Anonymous][quote=Anonymous]It sounds like the FAQ is misleading, either in referring to a deferre acceptance algorithm or in repeatedly referring to a single "lottery number." If someone invoved in the process is reading this can they please change the FAQ so it is accurate and clear? Unlike some of the pps I do not "trust" an explanation posted anonymously on a message board by someone claiming to have insider knowledge.[/quote]

The FAQ is correct. There is a deferred acceptance algorithm and there is a single lottery number (which is not the same as the tracking number).

Deferred acceptance is required whenever the preference for all students is not the same at every school. If the preference is the same at every school, you just start with the highest-ranked lottery number, assign them to their top-ranked school, and go from there. However, if different students are ranked differently by different schools, you have to have deferred acceptance.  There are two ways this can happen. One is if each school does its own drawing. That is not the way DC works. The other is if all schools use the same lottery number, but each school has its own preferences that supercede lottery numbers (in-boundary, sibling, proximity). Those preferences are school-specific, so your rank at various schools is different, even with the same lottery number. That is how DC works.

Another poster keeps talking about the trades that New Orleans does. Trades are not possible when using Gale-Shapley deferred acceptance. Gale-Shapley is a "stable" solution, by definition a stable solution one in which trades are impossible.  From the wikipedia article:

"a matching is stable when there does not exist any alternative pairing (A, B) in which both A and B are individually better off than they would be with the element to which they are currently matched."

http://en.wikipedia.org/wiki/Stable_marriage_problem[/quote]

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