docs: protected void sparsify()
      {
          final int N = vecs.size();
          int accSize = accelCache == null ? 0 : accelCache.size()/N;
          int svCount = 0;
          for(int i = 0; i < N; i++)
              if(alphas[i] != 0)//Its a support vector
              {
                  ListUtils.swap(vecs, svCount, i);
                  if(accelCache != null)
                      for(int j = i*accSize; j < (i+1)*accSize; j++)
                          ListUtils.swap(accelCache, svCount*accSize+j-i*accSize, j);
                  alphas[svCount++] = alphas[i];
              }
  
          vecs = new ArrayList<Vec>(vecs.subList(0, svCount));
          alphas = Arrays.copyOfRange(alphas, 0, svCount);
      }