iVector相关代码详解

# ivector-normalize-length

将iVectors长度归一化，并乘上缩放因子sqrt(feature-dimension)

Usage:  ivector-normalize-length [options] <ivector-rspecifier> <ivector-wspecifier>
e.g.:
 ivector-normalize-length ark:ivectors.ark ark:normalized_ivectors.ark

Options:
  --normalize: Set this to false to disable normalization (bool, default = true)
  --scaleup: 归一化后的vec的缩放因子为'sqrt(dim)' (bool, default = true)

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int main(int argc, char *argv[]) {
  using namespace kaldi;
  typedef kaldi::int32 int32;
  try {
    ParseOptions po(usage);
    bool normalize = true;

    po.Register("normalize", &normalize,
                "Set this to false to disable normalization");

    bool scaleup = true;
    po.Register("scaleup", &scaleup,
                "If 'true', the normalized iVector is scaled-up by 'sqrt(dim)'");

    po.Read(argc, argv);

    if (po.NumArgs() != 2) {
      po.PrintUsage();
      exit(1);
    }

    std::string ivector_rspecifier = po.GetArg(1),
        ivector_wspecifier = po.GetArg(2);


    int32 num_done = 0;

    double tot_ratio = 0.0, tot_ratio2 = 0.0;

    SequentialBaseFloatVectorReader ivector_reader(ivector_rspecifier);
    BaseFloatVectorWriter ivector_writer(ivector_wspecifier);


    for (; !ivector_reader.Done(); ivector_reader.Next()) {
      std::string key = ivector_reader.Key();
      Vector<BaseFloat> ivector = ivector_reader.Value();
      BaseFloat norm = ivector.Norm(2.0); // L2-norm，取绝对值之和并开根
      BaseFloat ratio = norm / sqrt(ivector.Dim()); // 它比正常情况下的预期值大多少
      if (!scaleup) ratio = norm;

      KALDI_VLOG(2) << "Ratio for key " << key << " is " << ratio;
      if (ratio == 0.0) {
        KALDI_WARN << "Zero iVector";
      } else {
        if (normalize) ivector.Scale(1.0 / ratio);
      }
      ivector_writer.Write(key, ivector);
      tot_ratio += ratio;
      tot_ratio2 += ratio * ratio;
      num_done++;
    }

    KALDI_LOG << "Processed " << num_done << " iVectors.";
    if (num_done != 0) {
      BaseFloat avg_ratio = tot_ratio / num_done,
          ratio_stddev = sqrt(tot_ratio2 / num_done - avg_ratio * avg_ratio);
      KALDI_LOG << "Average ratio of iVector to expected length was "
                << avg_ratio << ", standard deviation was " << ratio_stddev;
    }
    return (num_done != 0 ? 0 : 1);
  } catch(const std::exception &e) {
    std::cerr << e.what();
    return -1;
  }
}

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为什么与sqrt(dim)有关？可能如果特征数过多，会导致数值无穷小，所以再乘以缩放因子
为什么有个--normalize的开关，本来就是归一化函数，也不会有人选false吧？

#Kaldi

上次更新: 2024/04/10, 22:12:29

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