Question

x=4
y=0
numguesses=0
epsilon=.0001
tupofnum = [-13.39, 0.0, 17.5, 3.0, 1.0]
strofnum=tupofnum
n=numguesses=0
finalans=[]
while x>=epsilon and x>=0:
test=x-(evaluate_poly(tupofnum,x)/(evaluate_poly(compute_deriv(strofnum),x)))
test=round(test,4)
if test<0:
break
else:
print test
numguesses+=1
x=test
finalans=(test,numguesses)

print finalans
my code for finding the f(x_0) using newtons successive approximation method. however I get a different final answer for different values of x to start at. is my code wrong?

Answer 1

def evaluate_poly(tupofnum, x):
"""
Computes the polynomial function for a given value x. Returns that value.
"""
global y
i=0
while i<len(tupofnum):
for b in tupofnum:
if tupofnum[i]==b and b>0:
#print tupofnum[i],'tupofnum','index= ',i,'x=',x #debugging print
y+=(x**i)*b
i+=1
#print 'result of evaluate)poly-',y
return y

Answer 2

def compute_deriv(strofnums):
"""
Computes and returns the derivative of a polynomial function. If the
derivative is 0, returns (0.0,)."""
i=0
y=0
global result
while i <len(strofnums):
strofnums[i]=strofnums[i]*i
result= strofnums[1:len(strofnums)]
#print 'i- ',i
#print "strofnums-",strofnums

i+=1
#print 'result compute_deriv-',result
return result

Answer 3

ok discovered that for using the function eval_poly in an iteration, I needed to set y=0 at the beginning of each function call or it would continuously add every result to y of each iteration of the main while loop heheheheh. big difference.

Answer 4

Yah, that would be a difference!

Just as a note, there are a couple things you can do you make code paste better here. For one, ask the question part in thew question, then post the code in the next message with a ``` above and below it. That makes a code block like:

```
def evaluate_poly(tupofnum, x):
""" Computes the polynomial function for a given value x. Returns that value. """
global y
i=0
while i<len(tupofnum):
for b in tupofnum:
if tupofnum[i]==b and b>0:
#print tupofnum[i],'tupofnum','index= ',i,'x=',x #debugging print
y+=(x**i)*b
i+=1
#print 'result of evaluate)poly-',y
return y
```

If you try and copy and paste it without the ``` it collapses, but that version can be copied and pasted fine.

There are also code pasting services for larger chunks of code, like pastebin and dpaste.

http://pastebin.com/
http://dpaste.com/

I really like dpaste for simple things that only need to be around for a while.

Answer 5

ok so , instructions are:
ask the query in the first block, then in reply to my query, I can deliver the code, if I have ``` before the code and after such as......
```def compute_deriv(strofnums):
"""
Computes and returns the derivative of a polynomial function. If the
derivative is 0, returns (0.0,)."""
i=0
y=0
global result
while i <len(strofnums):
strofnums[i]=strofnums[i]*i
result= strofnums[1:len(strofnums)]
#print 'i- ',i
#print "strofnums-",strofnums

i+=1
#print 'result compute_deriv-',result
return result
```