Newton Method, type issue

Question

a=input("Write your function")
b=input("Input the derivative of your function ")

def f(x):
   return a

def fprime(x):
   return b


guess= 1
for n in range(1, 100):
   nextguess = guess - f(guess)/fprime(guess)
   print(nextguess)
   guess = nextguess

The error code:

Traceback (most recent call last):
  File "C:\Users\Anton Morian\kod\Projekt.py", line 13, in <module>
    nextguess = guess - f(guess)/fprime(guess)
TypeError: unsupported operand type(s) for /: 'str' and 'str'

The error message is telling you the division operator expects numbers but is getting strings. Shouldn’t be hard to see where it gets strings from. — Nathan Hughes, Mar 25 '18 at 02:23
In other words, `a` and `b` are strings, and strings cannot be divided. — DYZ, Mar 25 '18 at 02:26
Your use of function is useless. You can directly use a and b as variable. — Rahul, Mar 25 '18 at 02:44
Possible duplicate of [How can I read inputs as integers?](https://stackoverflow.com/questions/20449427/how-can-i-read-inputs-as-integers) — Jongware, Mar 25 '18 at 02:49
"Write your function" doesn't do what you think it does. If I give it `2x + 1`, `f(23)` will return the string `2x + 1`. You don't do math on a string. — Bailey Parker, Mar 25 '18 at 03:47

score 0 · Answer 1 · answered Mar 25 '18 at 02:46

First, you dont need funtions here. Second, input() in python returns str. You neet to convert it to int to do math.

I am not a math guy so dont knos what you trying to achieve here but try this code.

a=input("Write your function")
b=input("Input the derivative of your function ")

guess= 1
for n in range(1, 100):
   nextguess = guess - int(a)/int(b)
   print(nextguess)
   guess = nextguess

score 0 · Answer 2 · answered Mar 27 '18 at 15:53

This is my final result, what do u think? And yes I am aware of using global varibles.

And btw, its newtows method

restart = True
import re
from decimal import Decimal
while restart:
  print("Hej ska du vara! Detta är Newtons metod. Jag kan räkna ut nollställen ALLA nollställen, coolt va?!? Testa gärna mig :)")
  a=(input("Skriv din funktion"))
  b=(input("Ange dervatan till din funktion"))

  def f(x):
     return eval(re.sub("x", str(x), a))

  def fprime(x):
     return eval(re.sub("x", str(x), b))

  gissa = None
  inputText = "Ange din gissning av ett nollställe: "

  def getInput():
      global gissa
      global inputText
      gissa = float(input(inputText))

      if fprime(gissa) == 0:
          inputText = "Gissningen ej definierad, ange en ny: "
          return True
      else:
          return False

  while getInput():
      pass

  for n in range(1, 50):
      nextgissa = gissa - f(gissa)/fprime(gissa)
      gissa = nextgissa

  gissa=Decimal(gissa)
  output=round(gissa,2)
  print("Nollstället är", output)
  restart=input("Tryck på valfri tagent för att starta om eller enter för att avsluta!")
  if restart=="":
      restart = False
      print("Hejdå ska du vara!")

Newton Method, type issue

2 Answers2