CODEWITHSUNDEEP
pythonrecursion
facha
facha

Reputation: 12512

Can't figure out a recursive function

I have this piece of code to calculate first and second derivatives of a function at a given point

def yy(x):
   return 1.0*x*x

def d1(func, x ,e):
    x = x
    y = func(x)
    x1 = x + e
    y1 = func(x1)
    return 1.0*(y - y1)/(x - x1)

def d2(func ,x, e):
    x = x
    y = d1(func, x, e)
    x1 = x + e
    y1 = d1(func, x1, e)
    return 1.0*(y - y1)/(x - x1)

yy is the actual function. d1 and d2 functions that calculate the 1st and 2nd derivatives. They are the ones I'm interested in optimizing. As you can see they both have almost the same code. I could basically keep writing functions like that for 3rd, 4th, etc derivatives, however I'm wondering if it is possible to write it as a single function specifying the derivative level as a parameter.

Upvotes: 4

Views: 349

Answers (2)

Anubhav C
Anubhav C

Reputation: 2651

def deriv(func, order, x, e):
    if order < 0: raise ValueError
    if order == 0: return func(x)
    y = deriv(func, order-1, x, e)
    x1 = x + e
    y1 = deriv(func, order-1, x1, e)
    return float(y - y1)/(x - x1)

order = 1 gives the first derivative, order = 2 gives the 2nd, and so on.

Upvotes: 4

tylert
tylert

Reputation: 301

Try this, where lvl is derivative level. 

def d(func, x ,e, lvl):
    x1 = x + e

    if lvl == 1:
        x = x
        y = func(x)
        y1 = func(x1)
        return 1.0*(y - y1)/(x - x1)
    else:
        return 1.0*(d(func, x, e, lvl-1) - d(func, x1, e, lvl-1) )/(x-x1)

Upvotes: 1

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