Question

Hi..in python 6.00 Problem set 2, Implementing newton's method, problem 2, on running the solution code for this, i am not getting answer as expected. Any one else facing same problem? Why is it coming?

Answer 1

Actually its problem 3 in problem set 2...

Answer 2

Were you receiving an error, or it is calculating it incorrectly? The solution code I downloaded from the OCW website needed the compute_root function definition body indented. I also had to change the print statements in evaluate_poly and compute_deriv to return statements.

Answer 3

def compute_root(poly, x_0, epsilon):

#define root to make code simpler.
root = evaluate_poly(poly,x_0)
iterations = 0

#until root (evaluate_poly) is within our error range of 0...
while (root > epsilon) or (root < -epsilon):
#...apply newton's method, calculate new root, and count iterations.
x_0 = (x_0 - ((root)/(evaluate_poly(compute_deriv(poly),x_0))))
root = evaluate_poly(poly,x_0)
iterations = iterations + 1
return (x_0,iterations)

Running this returns -13.2119
(-0.0, 0.0, 35.0, 9.0, 4.0) which is different from expected result (0.80679075379635201, 8.0) . Am I missing something here?

Answer 4

Hi Theeconomist, thanks for your reply. I am also getting this error:
Traceback (most recent call last):
File "<pyshell#15>", line 1, in <module>
compute_root(poly, x_0, epsilon)
File "C:\Documents and Settings\Administrator\Desktop\ps2-sol\ps2_newton.py", line 41, in compute_root
x_0 = (x_0 - ((root)/(evaluate_poly(compute_deriv(poly),x_0))))
File "C:\Documents and Settings\Administrator\Desktop\ps2-sol\ps2_newton.py", line 11, in evaluate_poly
for i in range(0,len(poly)):
TypeError: object of type 'NoneType' has no len()