CODEWITHSUNDEEP
pythonpython-3.xnumpypolynomials
Squishy
Squishy

Reputation: 96

Write numpy's polyval() function

I am trying to write a function that can replicate the numpy function, np.polyval()

here is my current code:

def eval(poly, x):
    result = 0  
    for i in poly:
      y = (x ** (len(poly) - poly.index(i)-1))
      result += y
  return result

poly is supposed be a list formatted for the numpy.poly1d function

but the problem with this code, is when x is equal to a negative number

can someone help me with this code?

Upvotes: 0

Views: 545

Answers (2)

Aryan Garg
Aryan Garg

Reputation: 117

Hey I found this snippet of code to work similar to np.polyval() function:

def poly(polynomial: list,value: int):
    final = 0
    for i in range(len(polynomial)):
        final += (value**i)*polynomial[(-1*i)-1]
    return final

Explanation using an example: poly([1,-5,5],-3)

range(len(polynomial)) returns 0,1,2 per iteration. those are also the powers we need for the quadratic equation. The (value**i)*polynomial[(-1*i)-1] expression takes our value (in this case -3) and gives it the value of i (i.e (-3)^0,(-3)^1,(-3)^2). and then multiplies it with polynomial[(-1*i)-1]th index of the list provided. (-1 when i=0;-2 when i=1 and -3 when i=2).

Finally it adds all of this together and returns a value.

Upvotes: 1

deltascience
deltascience

Reputation: 3380

Have you tried math.pow function ?

import math
def func(poly, x):
  result=0
  i=1
  for p in poly:
    result += p*math.pow(x, len(poly)-i)
    i+=1
  return result

This is from numpy.polyval page:

If p is of length N, this function returns the value:

p[0]*x**(N-1) + p[1]*x**(N-2) + ... + p[N-2]*x + p[N-1]

Upvotes: 0

Related Questions