def _num_items_2_heatmap_one_day_figsize(n):
    """ uses linear regression model to infer adequate figsize
        from the number of items 
    Data used for training:
        X = [2,4,6,10,15,20,30,40,50,60]
        y = [[10,1],[10,2],[10,3],[10,4],[10,6],[10,8],[10,10],[10,12],[10,15],[10,17]]
    Parameters
    ----------
    n : int
        number of items
    Returns
    -------
    (w,h) : tuple
        the width and the height of the figure
    """
    w = 10
    h = 0.27082*n + 1.38153 
    return (int(w), int(h))