File:Runge phenomenon.svg

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Summary

Description
English: The red curve is the Runge function.

The blue curve is a 5th-order interpolating polynomial (using six equally spaced interpolating points). The green curve is a 9th-order interpolating polynomial (using ten equally spaced interpolating points).

At the interpolating points, the error between the function and the interpolating polynomial is (by definition) zero. Between the interpolating points (especially in the region close to the endpoints 1 and −1), the error between the function and the interpolating polynomial gets worse for higher-order polynomials.
Español: La curva roja es la función de Runge.

La curva azul es un polinomio interpolante de orden 5 (usando seis puntos equiespaciados). La curva verde es un polinomio interpolante de orden 9 (usando diez puntos equiespaciados).

A los puntos interpolantes el error entre la función y el polinomio interpolantes es cero (por definición). Entre estos puntos (especialmente cerca de los extremos 1 y -1) el error entre la función y el polinomio interpolante incrementa conforme el polinomio aumenta de orden.
Date
Source Own work
Author Nicoguaro
SVG development
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Source code
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Python code

from __future__ import division
import numpy as np
import matplotlib.pyplot as plt
from scipy.interpolate import lagrange
from matplotlib import rcParams

rcParams['font.family'] = 'serif'
rcParams['font.size'] = 16

def runge(x):
    return 1/(1 + 25*x**2)

plt.figure(figsize=(8,8))
npts = 201

# Runge Function
x_vec = np.linspace(-1, 1, npts)
y_vec = runge(x_vec)
plt.plot(x_vec, y_vec, lw=2, color='r')

# Fifth degree polynomial
pts_x = np.linspace(-1, 1, 6)
pts_y = runge(pts_x)
poly = lagrange(pts_x, pts_y)
y_interp = poly(x_vec)
plt.plot(x_vec, y_interp, lw=2, color='b')

# Ninth degree polynomial
pts_x = np.linspace(-1, 1, 10)
pts_y = runge(pts_x)
poly = lagrange(pts_x, pts_y)
y_interp = poly(x_vec)
plt.plot(x_vec, y_interp, lw=2, color='g') 

plt.savefig("Runge_phenomenon.svg")
plt.show()

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w:en:Creative Commons
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22 October 2015

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Date/TimeThumbnailDimensionsUserComment
current23:40, 22 October 2015Thumbnail for version as of 23:40, 22 October 2015720 × 720 (24 KB)NicoguaroUser created page with UploadWizard
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