Error: unsupported operand type(s) for -: 'list' and 'int'-CodePudding

I am attempting to make a plot using Chebyshev nodes and Lagrange polynomials shown in the following but I am receiving the error x, y, and format string must not be None. Why is this happening, how can I fix it/ plot what I want to appropriately?

EDIT: I have updated my code to fix the original error x, y, and format string must not be None and now I have the error unsupported operand type(s) for -: 'list' and 'int'

import numpy as np

def lagrange(x, z, f):
    d = len(x)
    if len(x) != len(z):
        print("Error: the length of x and z is different")
    else:
        p = 0
        for i in range (d):
            L = 1
            for j in range (d):
                if j != i:
                    L *= (z-x[j])/(x[i] - x[j])
                p  = f[i]*L
        return p
        

def f(x):
  return np.cos(x)

d = [0.1, 4, 0.2]
g = [-0.3, 0, 0.3]
lagrange(d, g, f(d))

CodePudding user response：

You can solve this by using np.array:

import numpy as np

def lagrange(x, z, f):
    d = len(x)
    if len(x) != len(z):
        print("Error: the length of x and z is different")
    else:
        p = 0
        for i in range (d):
            L = 1
            for j in range (d):
                if j != i:
                    L *= (z-x[j])/(x[i] - x[j])
                p  = f[i]*L
        return p
        

def f(x):
  return np.cos(x)


d = np.array([0.1, 4, 0.2])
g = np.array([-0.3, 0, 0.3])

lagrange(d, g, f(d))

This will return array([-5.08984891, 1.04582888, 6.70431625])