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numpymatplotlibappendattributeerrornewtons-method
user23143933
user23143933

Reputation: 3

How to solve a attribute error while making newton-methods in Python

I'm making a newton-raphson rule code with python, and there is a error which I don't know why it's occuring. Please help me.

import numpy as np
import matplotlib.pyplot as plt

def f(x):
    return x**2 - 10

def df(x):
    return 2*x

def newton_raphson(x0, f, df, tol=1e-10, max_iter = 100):
    x = x0
    iteration = 0
    x_values = x

    while np.abs(f(x)) > tol and iteration < max_iter:
        x = x - f(x) / df(x)
        x_values.append(x)
        iteration +=1

    return x_values

x_values = np.linspace(-5, 5, 100)
plt.plot(x_values, f(x_values), label = 'f(x) = $x**2 - 10')

roots = newton_raphson(4.0, f, df)
plt.scatter(roots, [0]*len(roots), color='gray', label= 'roots')

plt.xlabel('x')
plt.ylabel('f(x)')
plt.title('Newton-Raphson Method')
plt.axhline(0, color='black',linewidth=0.5)
plt.axvline(0, color='black',linewidth=0.5)
plt.grid(color = 'gray', linestyle = '--', linewidth = 0.5)
plt.legend()

plt.show

This is the code and I'm trying to find a roots of x**2 - 10

however, the error, which is saying 'AttributeError: 'float' object has no attribute 'append'' is occuring. Why is this problem taking place, and how can I solve this problem?

Upvotes: 0

Views: 52

Answers (1)

Oskar Hofmann
Oskar Hofmann

Reputation: 807

In your function newton_raphson() you define x as a copy of the value x0 and then define x_values as a copy of x. So x_values is a single float (= floating point number) to which you try to append values. This is not possible in Python. I assume x_values is meant to be an empty list:

def newton_raphson(x0, f, df, tol=1e-10, max_iter = 100):
    x = x0
    iteration = 0
    x_values = []

    while np.abs(f(x)) > tol and iteration < max_iter:
        x = x - f(x) / df(x)
        x_values.append(x)
        iteration +=1

    return x_values

Using this, your code works fine.

If you want x_values to contain the value x0 you must still define it as list with that value in it:

x_values = [x0]

Upvotes: 0

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