.. _program_listing_file_src_translator_beam_search.h:

Program Listing for File beam_search.h
======================================

|exhale_lsh| :ref:`Return to documentation for file <file_src_translator_beam_search.h>` (``src/translator/beam_search.h``)

.. |exhale_lsh| unicode:: U+021B0 .. UPWARDS ARROW WITH TIP LEFTWARDS

.. code-block:: cpp

   #pragma once
   
   #include "marian.h"
   #include "translator/history.h"
   #include "translator/scorers.h"
   
   namespace marian {
   
   class BeamSearch {
   private:
     Ptr<Options> options_;
     std::vector<Ptr<Scorer>> scorers_;
     size_t beamSize_;
     Ptr<const Vocab> trgVocab_;
   
     const float INVALID_PATH_SCORE;
     const bool PURGE_BATCH = true; // @TODO: diagnostic, to-be-removed once confirmed there are no issues.
   
     static float chooseInvalidPathScore(Ptr<Options> options) {
       auto prec = options->get<std::vector<std::string>>("precision", {"float32"});
       auto computeType = typeFromString(prec[0]);
       return NumericLimits<float>(computeType).lowest;
     }
   
   public:
     BeamSearch(Ptr<Options> options, const std::vector<Ptr<Scorer>>& scorers, const Ptr<const Vocab> trgVocab)
         : options_(options), scorers_(scorers), beamSize_(options_->get<size_t>("beam-size")), trgVocab_(trgVocab),
           INVALID_PATH_SCORE{chooseInvalidPathScore(options)}
     {}
   
     // combine new expandedPathScores and previous beams into new set of beams
     Beams toHyps(const std::vector<unsigned int>& nBestKeys, // [currentDimBatch, beamSize] flattened -> ((batchIdx, beamHypIdx) flattened, word idx) flattened
                  const std::vector<float>& nBestPathScores,  // [currentDimBatch, beamSize] flattened
                  const size_t nBestBeamSize, // for interpretation of nBestKeys
                  const size_t vocabSize,     // ditto.
                  const Beams& beams,
                  const std::vector<Ptr<ScorerState /*const*/>>& states,
                  Ptr<data::CorpusBatch /*const*/> batch, // for alignments only
                  Ptr<class FactoredVocab/*const*/> factoredVocab, size_t factorGroup,
                  const std::vector<bool>& dropBatchEntries, // [origDimBatch] - empty source batch entries are marked with true, should be cleared after first use.
                  const std::vector<IndexType>& batchIdxMap) const;
   
     std::vector<float> getAlignmentsForHypothesis( // -> P(s|t) for current t and given beam and batch dim
         const std::vector<float> alignAll, // [beam depth, max src length, batch size, 1], flattened vector of all attention probablities
         Ptr<data::CorpusBatch> batch,
         int beamHypIdx,
         int currentBatchIdx,
         int origBatchIdx,
         int currentDimBatch) const;
   
     // remove all beam entries that have reached EOS
     Beams purgeBeams(const Beams& beams, /*in/out=*/std::vector<IndexType>& batchIdxMap);
   
     // main decoding function
     Histories search(Ptr<ExpressionGraph> graph, Ptr<data::CorpusBatch> batch);
   };
   
   }  // namespace marian