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Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

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Colorless Green.

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Cache rewrite.

Extending OpenSSH.

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Using Choco

From: andrew cooke <andrew@...>

Date: Fri, 30 Mar 2012 23:27:34 -0300

I just finished (before midnight!) a solution to
http://stackoverflow.com/questions/9689436 using Choco
http://www.emn.fr/z-info/choco-solver/

And it's pretty neat.

Previously, I had written a simple depth-first search and a "smart" search
with constraint propagation (along the same lines as
http://norvig.com/sudoku.html).  My DFS was fast when there were few
constraints while my "smart" routine was fast when there were lots of
constraints.  But both were disappointing when not well-matched to the
problem.

In contrast, Choco combines the best of both worlds (although the initial
startup cost is higher).  It's as fast as a simple DFS when it needs to be,
but can also exploit constraints to find quick results when possible.

Which I guess is what you'd expect.

The downside is that it's a big system, and the API docs aren't so great.
There's a manual, which is a good introduction, but when you start to explore
it can become a little opaque.  For example: it turns out that (as far as I
can tell) if you specify a set of values for a variable, they need to be
ordered.  That's not in the API docs, but without it, the system crashes.

Even so, the speed is impressive.

Andrew

PS Choco is Java, but I called it from Clojure.  I really like Clojure - it
seems to hit the sweet spot of functional, untyped and, surprisingly
important, good control over evaluation strategies (lazy and eager).  It's
like a Haskell for dumb people :o)

Choco Update (and New Blog)

From: andrew cooke <andrew@...>

Date: Fri, 6 Apr 2012 20:00:40 -0300

Alas, the comments above were written in haste.  There was a bug (well,
several) in my code.  It turns out that Choco is not a magic bullet - in fact
it performs pretty much the same as my "smart" search.  Which isn't too bad or
surprising, really.

There is much, much more information in the links below, which are to a new
blog I have started with people at work.  I am not "moving" there, but will
use that to document work that involves company time (as this did - although
it also sucked up a lot of my own time, too).

 http://isti.bitbucket.org/2012/04/01/pipes-clojure-choco-1.html
 http://isti.bitbucket.org/2012/04/02/pipes-clojure-choco-2.html
 http://isti.bitbucket.org/2012/04/04/pipes-clojure-choco-3.html
 http://isti.bitbucket.org/2012/04/06/pipes-clojure-choco-4.html
 http://isti.bitbucket.org/2012/04/07/pipes-clojure-choco-5.html

Andrew

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