what if I don't know the feature names before hand? In that case, can I set the weights directly during decoding?
On Thu, Nov 13, 2014 at 4:59 PM, Barry Haddow <bhad...@staffmail.ed.ac.uk> wrote: > Hi Prashant > > You add something like this to your moses.ini: > > [weight-file] > /path/to/sparse/weights/file > > The sparse weights file has the form: > > name1 weight1 > name2 weight2 > name3 weight3 > . > . > . > > At least that's how it works in Moses v2. > > cheers - Barry > > On 13/11/14 15:42, Prashant Mathur wrote: > >> Thanks a lot Barry for your answers. >> >> I have another question. >> When I print these sparse features at the end of decoding, all sparse >> features are assigned a weight of 0 because all of them were initialized >> during decoding. >> How can I set these weights for sparse features before they are evaluated? >> >> >> Thanks Hieu for the link.. >> I am going to update the code as soon as I can.. but it will take some >> time.. will get back to you when I do that. >> >> --Prashant >> >> >> On Thu, Nov 13, 2014 at 2:34 PM, Hieu Hoang <hieu.ho...@ed.ac.uk <mailto: >> hieu.ho...@ed.ac.uk>> wrote: >> >> re-iterating what Barry said, you should use the github moses if >> you want to create your own feature functions, especially with >> sparse features. The reasons: >> 1. Adding new feature functions is a pain in v 0.91. It's >> trivial now. You can watch my talk to find out why >> http://lectures.ms.mff.cuni.cz/video/recordshow/index/44/184 >> 2. It's confusing exactly when the feature functions are >> computed. It's clear now (hopefully!) >> 3. I think you had to set special flags somewhere to use sparse >> features. Now, all feature functions can use sparse features as >> well as dense features >> 4. I don't remember the 0.91 code very well. So I can't help you >> if you get stuck >> >> >> On 13 November 2014 11:06, Barry Haddow >> <bhad...@staffmail.ed.ac.uk <mailto:bhad...@staffmail.ed.ac.uk>> >> >> wrote: >> >> Hi Prashant >> >> I tried to answer your questions inline: >> >> >> On 12/11/14 20:27, Prashant Mathur wrote: >> > Hi All, >> > >> > I have a question about implementing sparse feature function. >> > I went through the details on its implementation, still >> somethings are >> > not clear. >> > FYI, I am using an old version of moses which dates back to >> Release >> > 0.91 I guess. So, I am sorry if my questions don't relate to the >> > latest implementation. >> >> This is a bad idea. The FF interface has changed a lot since 0.91. >> >> > >> > 1. I was looking at the TargetNgramFeature where >> MakePrefixNgrams adds >> > features in Evaluate function. From the code it seems >> MakePrefixNgrams >> > is adding sparse features on the fly. Is it correct? >> >> Yes, you can add sparse features on the fly. That's really >> what makes >> them sparse features. >> >> > >> > what is the weight assigned to this newly added feature? 1 or 0? >> >> The weight comes from the weights file that you provide at >> start-up. If >> the feature is not in the weights file, then it gets a weight >> of 0. >> >> > >> > 2. What is the difference between these two functions? >> > >> > /void PlusEquals(const ScoreProducer*sp, const std::string& >> name, >> > float score)/ >> > / >> > / >> > /void SparsePlusEquals(const std::string& full_name, float >> score) >> > / >> >> In the first, a string from the ScoreProducer is prepended to >> the name, >> whilst in the second the string full_name is used as the name. >> I think >> we should really use the first form to keep features in their own >> namespace, but the second form has pervaded Moses. >> >> > >> > It seems like both of them are used for updating sparse feature >> > values.. correct? >> > Or, do the first one points to sparse features of a >> particular FF and >> > second one to generic sparse features? >> > >> > 3. How is the structure like if I use one >> StatelessFeatureFunction >> > with unlimited scores? Is it different from having unlimited >> sparse >> > features? >> > >> > I assume if there is one FF then there is one weight >> assigned to it >> > but in the case of sparse features I have one weight for >> each feature. >> FFs can be dense or sparse. What that really means is that the >> number of >> feature values for a dense FF is known in advance (and so space is >> allocated in the feature value array) but for sparse FFs the >> number of >> feature values are not known in advance. So even dense FFs can >> have >> several weights associated with them - e.g. the phrase table >> features. >> In more recent versions of Moses a given FF can have both >> dense and >> sparse values. >> >> > >> > 4. In general when should I compute the sparse features? >> >> In general, computing them as soon as you can will probably >> make your >> code more efficient. When you are able to compute your sparse >> feature >> depends on the feature itself. For example, if the feature >> depends on >> only on the phrase pair then it could be computed and stored >> in the >> phrase table. This makes the phrase table bigger (which could >> slow you >> down) but saves on computation at decoding. On the other hand, >> a sparse >> reordering feature has to be mainly computed during decoding, >> since we >> do not know the ordering of segments until decoding. When I >> implemented >> sparse reordering features though, I precomputed the feature >> names since >> you don't want to do string concatenation during decoding. >> >> >> cheers - Barry >> >> > >> > Thanks for the patience, >> > --Prashant >> > >> > PS: I am still trying to figure out stuff, so questions >> might seem stupid. >> > >> > >> > _______________________________________________ >> > Moses-support mailing list >> > Moses-support@mit.edu <mailto:Moses-support@mit.edu> >> > http://mailman.mit.edu/mailman/listinfo/moses-support >> >> >> -- >> The University of Edinburgh is a charitable body, registered in >> Scotland, with registration number SC005336. >> >> _______________________________________________ >> Moses-support mailing list >> Moses-support@mit.edu <mailto:Moses-support@mit.edu> >> http://mailman.mit.edu/mailman/listinfo/moses-support >> >> >> >> >> -- Hieu Hoang >> Research Associate >> University of Edinburgh >> http://www.hoang.co.uk/hieu >> >> >> > > -- > The University of Edinburgh is a charitable body, registered in > Scotland, with registration number SC005336. > >
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