## TuringTest 2 years ago Python: Newston-Raphson I am getting too many iterations and my answer is off in the millions decimal place. Any ideas?

1. TuringTest

poly=(-13.39,0.0,17.5,3.0,1.0) x=0.1 epsilon=0.001 def evaluate_poly(poly, x): #evaluates a polynomial input as a tuple for a specific x value value=0 power=0 for i in poly: value+=i*x**power power+=1 return value def compute_derivative(poly): #returns a tuple representing the derivative #of the input polynomial as a tuple power=0 deriv=() for i in poly: deriv+=(i*power,) power+=1 return deriv def compute_root(poly, x, epsilon): #find the root of the polynomial poly using #Newton-Raphson method iterations=0 deriv=compute_derivative(poly) derivValue=evaluate_poly(deriv, x) #evaluates the current x value of the derivative of the polynomial value=evaluate_poly(poly, x) while abs(value) > epsilon: value=evaluate_poly(poly, x) derivValue=evaluate_poly(deriv, x) x-=value/derivValue iterations+=1 return x, iterations #outputs a the root and number of iterations as a tuple I get an output of (0.80679329312..., 139) the answer is supposed to be (0.806790679..., 8) My answer for the root is darn close, but why so am I getting so many iterations? I tried debugging it but all the numbers seem normal on every iteration, I'm just not getting there fast enough somehow...

2. TuringTest

my answer is within epsilon of the given answer, so I'm really just worried about the iterations

A million decimal places.....? or the millionths place? :P

4. TuringTest

The millionth place, actually I had the wrong value for epsilon, it should have been 0.0001 with that correction I get (0.8067887806273476, 141) and the given answer is (0.80679075379635201, 8) Since my answer and the given answer differ by a number less than epsilon=0.0001 the answer is not what I'm worried about, it's the fact that my algorithm uses 141 iterations when it's only supposed to use 8 ! I'm going to do this painfully on paper and see if I can debug this to find which variable(s) is/are misbehaving.

is # a comment?

6. TuringTest

yes and never mind, problem solved!

7. ishesh

if the problem is solved could u pls giv me the soln??