def index_1d(row, col):
    """For a given row and column in a grid world, return the row that cell would appear on in the transition matrix.

    Parameters
    ----------
    row : int
        The row number. Indexing starts at 0.
    col : int
        The column number. Indexing starts at 0.

    Returns
    -------
    transition_row : int
        The row on the transition matrix the row and column would appear on.
    """
    max_cols = 9
    return row * max_cols + col