def decrease(sheet, element, index, decrease_rate, col, divide=True, bound=None
    ):
    """Decrease the value in the dataset at position index/col.

    Parameters
    ----------
    sheet : a :class:`Sheet` object
    element : str: 'cell' or 'face' or 'edge' or 'vert'
    index : index in the datasets[element]
    decrease_rate : rate use to divide value in the column col.
    col : column from element which apply decrease_rate.
    divide : bool: if true the current col value is divide by decrease_rate. If false it is substracted. Default divide.
    bound: lower limit of the modify value. Default None.
    """
    if divide:
        new_value = sheet.datasets[element].loc[index, col] / decrease_rate
    else:
        new_value = sheet.datasets[element].loc[index, col] - decrease_rate
    if bound is not None:
        if new_value >= bound:
            sheet.datasets[element].loc[index, col] = new_value
    else:
        sheet.datasets[element].loc[index, col] = new_value
