code: private Matrix<Double> generateRandomMatrix(final int nRows, final int nColumns) {
      final List<List<Double>> rows = new ArrayList<>(nRows);
      final Random random = new Random();
      for (int i = 0; i < nRows; i++) {
        final List<Double> row = new ArrayList<>(nColumns);
        for (int j = 0; j < nColumns; j++) {
          row.add(random.nextDouble());
        }
        rows.add(row);
      }
      return new RowMatrix(rows);
    }
docs: Generate a matrix with random values.
  @param nRows number of matrix's rows.
  @param nColumns number of matrix's columns.
  @return Matrix that consists of random values.