I should probably start by saying that I am relatively new to python, but I have coded in java and Matlab before.
In python, the code
def func(f):
return f
g = func(cos)
print(g(0))
gives the result
>1.0
as g now is defined as the cosine function.
I want to write a function that calculates the derivative of any provided function using a finite difference approach. The function is defined as
def derivator(f, h = 1e-8):
and would like to achieve the follwing:
g = derivator(cos)
print(g(0)) # should be about 0
print(g(pi/2)) # should be about -1
At the moment my derivator function looks like this
def derivator(f, h = 1e-8):
return (f(x+h/2)-f(x-h/2))/h
which definitely is wrong, but I am not sure how I should fix it. Any thoughts?
Your current derivator() function (which should probably be called differentiator()) uses an undefined variable x and would return a single value, if x were defined--the value of f'(x). You want to return a function that takes an x value. You can define an inner function and return it:
def fprime(x):
return (f(x+h/2)-f(x-h/2))/h
return fprime
Because you don't use that function anywhere else, though, you can use lambda instead, which is also shorter:
return lambda x: (f(x+h/2)-f(x-h/2))/h
The only thing PEP 8 says about lambdas is that you should not assign the result of the lambda to a variable, then return it:
fprime = lambda x: (f(x+h/2)-f(x-h/2))/h # Don't do this!
return fprime