matplotlib fails in python3

Question

I want to render a 6th degree function with matplotlib, it works with this code i found, but not with python3.

import numpy as np
from matplotlib import pyplot as plt

def langrange_polynomial(X, Y):
    def L(i):
        return lambda x: np.prod([(x-X[j])/(X[i]-X[j]) for j in range(len(X)) if i != j]) * Y[i]
    Sx = [L(i) for i in range(len(X))]  # summands
    return lambda x: np.sum([s(x) for s in Sx])

# cut something

# Here i get the points with a function
(X, Y) = [1,2,3,4,5,6,7],[0,20,10,4,3,40,4]
F = langrange_polynomial(X, Y)

x_range = np.linspace(X[0], X[-1], 100)
plt.plot(X, Y, 'ro')
plt.plot(x_range, map(F, x_range))
plt.xlabel(r'$x$')
plt.ylabel(r'$F(x)$')
plt.title('Lagrange polynomial interpolation')
plt.grid(True)
plt.show()

Get this Error:

raise ValueError("x and y must have same first dimension")
ValueError: x and y must have same first dimension

in that Line:

plt.plot(x_range, map(F, x_range))

I read about something about declare the X,Y Coordinates to an np.array, but that did not worked anyway. What do I have to do in Python3.5?

ImportanceOfBeingErnest · Accepted Answer · 2017-02-25 19:01:32Z

1

In python 3, map(function, iterable) returns an iterator instead of a list.
You would need to get a list via

list(map(function, iterable))

or, more specifically in this case

plt.plot(x_range, list(map(F, x_range)))

answered Feb 25, 2017 at 19:01

ImportanceOfBeingErnest

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1 Comment

Benny H. Over a year ago

would have never guessed that ;-) Thanks alot!

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