class DoubleMatrix implements Matrix, Serializable, ImmutableBean {

  public static DoubleMatrix identity(int size) {
    if (size == 0) {
      return EMPTY;
    }
    double[][] array = new double[size][size];
    for (int i = 0; i < size; i++) {
      array[i][i] = 1d;
    }
    return new DoubleMatrix(array, size, size);
  }

    DoubleMatrix(double[][] data, int rows, int columns);
  @ImmutableConstructor private  DoubleMatrix(double[][] array);

}