docs: protected static double[][] means(List<? extends DBIDs> clusters, double[][] means, Relation<? extends NumberVector> relation) {
      if(TypeUtil.SPARSE_VECTOR_FIELD.isAssignableFromType(relation.getDataTypeInformation())) {
        @SuppressWarnings("unchecked")
        Relation<? extends SparseNumberVector> sparse = (Relation<? extends SparseNumberVector>) relation;
        return sparseMeans(clusters, means, sparse);
      }
      return denseMeans(clusters, means, relation);
    }