Hi Per, the -stack option controls histogram pruning in moses_chart. It's always on and the default stack size is 200 (the same as for phrase-based).
If your model is hierarchical or tree-to-string (i.e. no target syntax) then there will be up to two stacks per chart cell: one for X hypotheses and one for S hypotheses. If your model has target syntax then there can potentially be many stacks per cell (one for each distinct LHS label for the hypotheses that cover the span). The pop limit is applied on a per-cell basis and controls the number of hypotheses popped from the cube pruning queue (assuming you're using cube pruning, of course). Once a hypothesis is popped it's added to one of the chart cell's stacks, chosen according to the hypothesis' label. If the stack already contains one or more hypotheses with identical LM state values then the hypotheses are merged into a single stack entry (hypothesis recombination). Finally, the stack is pruned so that it doesn't exceed the maximum number of entries. The default pruning values are probably fine for most models. If you're using both source and target syntax then translation quality is likely to be substantially worse than phrase-based due to syntactic divergence. Solutions for this problem have been proposed in the literature (e.g. David Chiang's "Learning to Translate with Source and Target Syntax" in ACL 2010) but haven't made it into Moses yet. Results for string-to-tree or tree-to-string should be closer to phrase-based. Hope that helps... Phil On 18 Jun 2013, at 17:49, Kenneth Heafield <[email protected]> wrote: > There are a few kinds of pruning in syntactic decoding: > > -ttable-limit sets the max number of target side rules per source rule. > > -cube-pruning-pop-limit controls the beam size aka pop limit even if the > algorithm isn't cube pruning. Default 1000. > > I think the parser can also throw out entire source side matches. This > is disabled by default; ask Phil Williams about it. > > Kenneth > > On 06/18/13 12:36, Per Tunedal wrote: >> Hi, >> Is histogram pruning always on? What's the default stack size? Why isn't >> it listed among the settings on the Syntax Tutorial page? >> >> How is the search and pruning actually done for hierarchical models? >> When is the histogram pruning done? >> >> I've tested with the settings: >> moses_chart -f trainTreeSyntaxInSourceAndTarget/model/moses.ini < >> fr-sv.test.fr > fr-sv.test.fr.TreeSyntaxInSourceAndTarget.translated 2> >> stderrTreeSyntaxInSourceAndTarget.txt >> >> I suppose I got the default cube-pruning-pop-limit 1000, but what about >> the histogram pruning? I've read that the stack size isn't much of a >> problem when using cube pruning (Advanced Features page). >> >> BTW The results are very disappointing. >> >> Yours, >> Per Tunedal >> >> PS I've read a lot of books and papers on the subject but got lost in >> the details. A very simplified explanation with the main steps for the >> implementation in Moses would be helpful. >> >> On Tue, Jun 18, 2013, at 17:08, Hieu Hoang wrote: >>> there is historgram pruning in the chart decoder. It's implemented in >>> ChartHypothesisCollection::PruneToSize() >>> there is no threshold pruning >>> >>> >>> On 17 June 2013 21:14, Per Tunedal <[email protected]> wrote: >>> >>>> >>>> Hi, >>>> I can't find any settings for e.g. histogram pruning for the >>>> chart-decoder. Is cube pruning the only pruning used by Moses >>>> chart-decoder? >>>> When using cube pruning with a phrase model I suppose both threshold >>>> pruning and histogram pruning are used as well. The cube pruning only >>>> affects what new hypothesis to add to the stack, if I've understood the >>>> Advanced Features page correctly. >>>> Have I missed something? >>>> Yours, >>>> Per Tunedal >>>> _______________________________________________ >>>> Moses-support mailing list >>>> [email protected] >>>> http://mailman.mit.edu/mailman/listinfo/moses-support >>>> >>> >>> >>> >>> -- >>> Hieu Hoang >>> Research Associate >>> University of Edinburgh >>> http://www.hoang.co.uk/hieu >> _______________________________________________ >> Moses-support mailing list >> [email protected] >> http://mailman.mit.edu/mailman/listinfo/moses-support >> > _______________________________________________ > Moses-support mailing list > [email protected] > http://mailman.mit.edu/mailman/listinfo/moses-support _______________________________________________ Moses-support mailing list [email protected] http://mailman.mit.edu/mailman/listinfo/moses-support
