lagrange2.py

from pylab import *

# avalia o polinomio interpolador usando polinomios de Lagrange
def interpolL(x,T):
    S=0.0
    for i in range(len(T)):
        prod=1.0
        for j in range(len(T)):
            if j==i: continue
            prod=prod*(x-T[j][0])/(T[i][0]-T[j][0])
        S=S+T[i][1]*prod
    return S
# defino a funcao a ser tabelada:
f= lambda x : 1/(1+x**2)

# A proxima funcao constri uma tabela de f

def tabela(n,f,a,b):
    x = linspace(a,b,n)
    T=[]
    for t in x :
        T=T+[(t,f(t))]
    return T

def runge():
    N=raw_input("Digite um inteiro: ")
    T=tabela(N,f,-5,5)
    p= lambda x: interpolL(x,T)
    z=linspace(-5,5,100)
    plot(z,p(z), z, f(z))
    grid()