def fvals_sqrt(x):
"""
Return f(x) and f'(x) for applying Newton to find a square root.
"""
f = x**2 - 4.
fp = 2.*x
return f, fp
def solve(fvals_sqrt, x0, debug_solve=True):
"""
Solves the sqrt function, using newtons methon.
"""
fvals_sqrt(x0)
x0 = x0 + (f/fp)
print x0
When I try to call the function solve, python returns:
NameError: global name 'f' is not defined
Obviously this is a scope issue, but how can I use f within my solve function?
You want this:
def solve(fvals_sqrt, x0, debug_solve=True):
"""
Solves the sqrt function, using newtons methon.
"""
f, fp = fvals_sqrt(x0) # Get the return values from fvals_sqrt
x0 = x0 + (f/fp)
print x0
You're calling fvals_sqrt() but don't do anything with the return values, so they are discarded. Returning variables won't magically make them exist inside the calling function. Your call should be like so:
f, fp = fvals_sqrt(x0)
Of course, you don't need to use the same names for the variables as are used in the return statement of the function you're calling.
Problem is that you're not storing the returned value from the function call anywhere:
f,fp = fvals_sqrt(x0)
You need to unfold result of fvals_sqrt(x0), with this line
f, fp = fvals_sqrt(x0)
Globally, you should try
def fvals_sqrt(x):
"""
Return f(x) and f'(x) for applying Newton to find a square root.
"""
f = x**2 - 4.
fp = 2.*x
return f, fp
def solve(x0, debug_solve=True):
"""
Solves the sqrt function, using newtons methon.
"""
f, fp = fvals_sqrt(x0)
x0 = x0 + (f/fp)
print x0
solve(3)
Result
>>>
3.83333333333
