问使用Numpy的多项式系数误差

EN

import numpy as np
from numpy.polynomial.polynomial import Polynomial,polyval
from numpy import array
import sys


x_vid = array([0.0, 50.0, 75.0, 100.0])
y_vid = array([0.0, 30.0, 55.0, 100.0])
pol = Polynomial.fit(x_vid, y_vid, 5) # The polynomial is OK!!

# I've written this, which should do what numpy.polynomial.polynomial.polyval 
# does, as a sanity check:
def test_polyval(polynomialInstance,xArray):
    # check that xArray is a numpy.ndarray, using ndarray.shape
    try:
        y = np.zeros(xArray.shape)
    except Exception as e:
        sys.exit('polyval error: %s'%e)

    # manually sum the polynomial terms on xArray
    for exp,c in enumerate(polynomialInstance.coef):
        y = y + c*x**exp

    return y

# Define some random x values for testing, in the range of points used
# for fitting:
x = np.random.rand(100)*100

# Compute, using our own polyval function, then Polynomial.polyval,
# and finally using numpy.polyval, making sure to reverse the
# coefficient order for the last:
y_test_polyval = test_polyval(pol,x)
y_Polynomial_polyval = polyval(x,pol.coef)
y_numpy_polyval = np.polyval(pol.coef[::-1],x)

# Make sure the two results are within machine epsilon:
if np.allclose(y_test_polyval,y_numpy_polyval) and \
        np.allclose(y_test_polyval,y_Polynomial_polyval):
    print 'Hurray!'