Question

I'm writing a code for the Secant Method for root finding, but my code makes an infinite code of the correct answer. Below is my code, how do I fix it?

def f(x):
return (x**6)+7*(x**5)-15*(x**4)-70*(x**3)+75*(x**2)+175*x-125

def secant():
p0=float(input('Enter an initial guess for the root '))
p1=float(input('Enter another guess '))
TOL=float(input('Enter a tolerance in decimal form '))
n=15
i=1
while i<=n:
p=p1-f(p1)*(p1-p0)/(f(p1)-f(p0))
if abs(p-p1)<TOL:
print(p)
else:
p0=p1
p1=p
i=i+1
else:
print(p)
return p
  
print(secant())

Answer 1

So the program is mainly not running since you are not getting out of the loop when the tolerance condition is met .

Also the i=i+1 statement should be outside the if-else statements since everytime the tolerance condition is met the program is not going to the else statements and thus your i was not increasing , therefore you were getting a infinite loop.

also the second else statement was a syntax error

all these have been fixed below.

def f(x):
return (x**6)+7*(x**5)-15*(x**4)-70*(x**3)+75*(x**2)+175*x-125

def secant():
p0=float(input('Enter an initial guess for the root '))
p1=float(input('Enter another guess '))
TOL=float(input('Enter a tolerance in decimal form '))
n=15
i=1
while i<=n:
    p=p1-(f(p1)*(p1-p0))/(f(p1)-f(p0))
    i=i+1
    if abs(p-p1)<TOL:
       print(p)
       break #added a break method here so that the loop breaks when tolerance is met
    else:
       p0=p1
       p1=p
       print(p) #no need for another else
return p

print(secant())