make_data: prepare data for a random graph
    Parameters:
        - n: number of vertices
        - prob: probability of existence of an edge, for each pair of vertices
    Returns a tuple with a list of vertices and a list edges.

def make_data(n,prob):
    """make_data: prepare data for a random graph
    Parameters:
        - n: number of vertices
        - prob: probability of existence of an edge, for each pair of vertices
    Returns a tuple with a list of vertices and a list edges.
       """
    V = range(1,n+1)
    E = [(i,j) for i in V for j in V if i < j and random.random() < prob]
    return V,E