docs: public static double[][] centerMatrix(final double[][] matrix) {
      // FIXME: implement more efficiently. Maybe in matrix class itself?
      final double[][] normalizingMatrix = new double[matrix.length][matrix[0].length];
      for(double[] row : normalizingMatrix) {
        Arrays.fill(row, 1.0 / matrix[0].length);
      }
      return times(plusEquals(minusEquals(minus(matrix, times(normalizingMatrix, matrix)), times(matrix, normalizingMatrix)), times(normalizingMatrix, matrix)), normalizingMatrix);
    }