def from_list(b,L):
    c = vector(QQ, len(L))
    j = 0
    for i in L:
        c[j]=b[i]
        j = j+1
    return c


def ratios(z,y):
    r = vector(QQ,len(z))
    for i in range(len(z)):
        if y[i]<0 :
            r[i]= (-z[i] / y[i])
        else:
            r[i] = -1 

    return r