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https://issues.apache.org/jira/browse/LUCENE-3094?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13033072#comment-13033072
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Simon Willnauer edited comment on LUCENE-3094 at 5/13/11 3:19 PM:
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was (Author: simonw):
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> optimize lev automata construction
> ----------------------------------
>
> Key: LUCENE-3094
> URL: https://issues.apache.org/jira/browse/LUCENE-3094
> Project: Lucene - Java
> Issue Type: Improvement
> Reporter: Robert Muir
> Fix For: 4.0
>
> Attachments: LUCENE-3094.patch, after.png, before.png
>
>
> in our lev automata algorithm, we compute an upperbound of the maximum
> possible states (not the true number), and
> create some "useless" unconnected states "floating around".
> this isn't harmful, in the original impl we did the Automaton is simply a
> pointer to the initial state, and all algorithms
> traverse this list, so effectively the useless states were dropped
> immediately. But recently we changed automaton to
> cache its numberedStates, and we set them here, so these useless states are
> being kept around.
> it has no impact on performance, but can be really confusing if you are
> debugging (e.g. toString). Thanks to Dawid Weiss
> for noticing this.
> at the same time, forcing an extra traversal is a bit scary, so i did some
> benchmarking with really long strings and found
> that actually its helpful to reduce() the number of transitions (typically
> cuts them in half) for these long strings, as it
> speeds up some later algorithms.
> won't see any speedup for short terms, but I think its easier to work with
> these simpler automata anyway, and it eliminates
> the confusion of seeing the redundant states without slowing anything down.
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