[plt-scheme] Reexpansion of modules

From: Noel Welsh (noelwelsh at yahoo.com)
Date: Mon Aug 21 16:38:51 EDT 2006

--- Matthias Felleisen <matthias at ccs.neu.edu> wrote:

> Someone else recently wrote to the list about writing
> code that  
> required serious performance improvements. I believe it
> had to do  
> with number crunching. If it was _you_, could you remind
> us of the  
> problems? -- Matthias

It was me.  My problem boils down to this: calculate in the
Viterbi path of a hidden Markov model (HMM) as quickly as
possible.  (My actual situation has some wrinkles, but the
slow part is essentially this, and the Viterbi algorithm
for HMMs is well known).  I don't have statistics yet (I'm
working on collecting them) but I expect Scheme arrays to
be significantly slow than C arrays (I expect ~4-10 times).
 When looking at runtimes in the order of hours or days
these constant factors make a significant difference.  The
additional wrinkle is that I want clear hackable code --
this is part of my research so I'll be making many changes
to it as I explore different algorithms.


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