Python numpy.poly1d()用法及代碼示例

numpy.poly1d(arr，root，var)：此函數有助於定義多項式函數。這使得將“natural operations”應用於多項式變得容易。

參數：
-> arr : [array_like] The polynomial coefficients are given in decreasing order of powers. If the second parameter (root) is set to True then array values are the roots of the polynomial equation.
For example- poly1d(3, 2, 6) = 3x² + 2x + 6
poly1d([1, 2, 3], True) = (x-1)(x-2)(x-3) = x³ - 6x² + 11x -6

-> root: [bool, optional] True means polynomial roots. Default is False.
-> var : variable like x, y, z that we need in polynomial [default is x].

Arguments:
c : Polynomial coefficient.
coef : Polynomial coefficient.
coefficients: Polynomial coefficient.
order : Order or degree of polynomial.
o : Order or degree of polynomial.
r : Polynomial root.
roots : Polynomial root.

返回： Polynomial and the operation applied

代碼1：解釋poly1d()及其參數

# Python code explaining 
# numpy.poly1d() 
  
# importing libraries 
import numpy as np 
  
# Constructing polynomial 
p1 = np.poly1d([1, 2]) 
p2 = np.poly1d([4, 9, 5, 4]) 
  
print ("P1:", p1) 
print ("\n p2:\n", p2) 
  
# Solve for x = 2 
print ("\n\np1 at x = 2:", p1(2)) 
print ("p2 at x = 2:", p2(2)) 
  
# Finding Roots 
print ("\n\nRoots of P1:", p1.r) 
print ("Roots of P2:", p2.r) 
  
# Finding Coefficients 
print ("\n\nCoefficients of P1:", p1.c) 
print ("Coefficients of P2:", p2.coeffs) 
  
# Finding Order 
print ("\n\nOrder / Degree of P1:", p1.o) 
print ("Order / Degree of P2:", p2.order)

輸出：

P1:  
1 x + 2

 p2:
    3     2
4 x + 9 x + 5 x + 4


p1 at x = 2: 4
p2 at x = 2: 82


Roots of P1: [-2.]
Roots of P2: [-1.86738371+0.j         -0.19130814+0.70633545j -0.19130814-0.70633545j]


Coefficients of P1: [1 2]
Coefficients of P2: [4 9 5 4]


Order / Degree of P1: 1
Order / Degree of P2: 3

代碼2：多項式的基本數學運算

# Python code explaining 
# numpy.poly1d() 
  
# importing libraries 
import numpy as np 
  
# Constructing polynomial 
p1 = np.poly1d([1, 2]) 
p2 = np.poly1d([4, 9, 5, 4]) 
  
print ("P1:", p1) 
print ("\n p2:\n", p2) 
  
print ("\n\np1 ^ 2:\n", p1**2) 
print ("p2 ^ 2:\n", np.square(p2)) 
  
p3 = np.poly1d([1, 2], variable = 'y') 
print ("\n\np3:", p3) 
  
  
print ("\n\np1 * p2:\n", p1 * p2) 
print ("\nMultiplying two polynimials:\n",  
       np.poly1d([1, -1]) * np.poly1d([1, -2]))

輸出：

P1:  
1 x + 2

 p2:
    3     2
4 x + 9 x + 5 x + 4


p1 ^ 2:
    2
1 x + 4 x + 4
p2 ^ 2:
 [16 81 25 16]


p3:  
1 y + 2


p1 * p2:
    4      3      2
4 x + 17 x + 23 x + 14 x + 8

Multiplying two polynimials:
    2
1 x - 3 x + 2