def myHorner(dd, xp, x):
    n = np.size(xp)
    q = dd
    for k in range(n-1,0, -1):
        q = dd[k-1]+q*(xp-x[k-1])
    return q


def comparaison(f,a,b,n):
    xx=np.linspace(a,b,n)
    vectab= np.linspace(a,b,n)
    for i in range(1,n):

        x1= a + (i-1)*(b-a)/(n-1)
        x2= (a+b)/2 + ((b-a)/2)*cos((2*i-1)*pi/(2*n))
        df1=diffdiv(x1 , f(x1))
        df2=diffdiv(x2 , f(x2))
        p1 = myhorner(df1,x1,xx)
        p2 = myhorner(df2,x2,xx)
        plt.figure(1)
        plt.subplot(211)
        vectF=f(vectab)
        plt.plot(vectF)
        plt.subplot(212)
        plt.plot(x1,p1,'o',color='red')
        plt.plot(x2,p2,'o',color ='blue')

    plt.show()