import numpy as np
import matplotlib.pyplot as plt

xxx = np.arange(0, 1000) # x值，此時(shí)表示弧度
yyy = np.sin(xxx*np.pi/180) #函數(shù)值，轉(zhuǎn)化成度

z1 = np.polyfit(xxx, yyy, 7) # 用7次多項(xiàng)式擬合，可改變多項(xiàng)式階數(shù)；
p1 = np.poly1d(z1) #得到多項(xiàng)式系數(shù)，按照階數(shù)從高到低排列
print(p1) #顯示多項(xiàng)式

yvals=p1(xxx) # 可直接使用yvals=np.polyval(z1,xxx)

plt.plot(xxx, yyy, '*',label='original values')
plt.plot(xxx, yvals, 'r',label='polyfit values')
plt.xlabel('x axis')
plt.ylabel('y axis')
plt.legend(loc=4) # 指定legend在圖中的位置，類似象限的位置
plt.title('polyfitting')
plt.show()

 A one-dimensional polynomial class.

  A convenience class, used to encapsulate "natural" operations on
  polynomials so that said operations may take on their customary
  form in code (see Examples).

  Parameters
  ----------
  c_or_r : array_like
    The polynomial's coefficients, in decreasing powers, or if
    the value of the second parameter is True, the polynomial's
    roots (values where the polynomial evaluates to 0). For example,
    ``poly1d([1, 2, 3])`` returns an object that represents
    :math:`x^2 + 2x + 3`, whereas ``poly1d([1, 2, 3], True)`` returns
    one that represents :math:`(x-1)(x-2)(x-3) = x^3 - 6x^2 + 11x -6`.
  r : bool, optional
    If True, `c_or_r` specifies the polynomial's roots; the default
    is False.
  variable : str, optional
    Changes the variable used when printing `p` from `x` to `variable`
    (see Examples).

xx=np.poly1d([1,2,3])
print(xx)
yy=xx**2 #求平方，或者用 xx * xx
print(yy)