问题
# import packages we need later
import matplotlib.pyplot as plt
import numpy as np
What I am doing
Inspired by this question & answer, I am fitting a series of Legendre polynomials to a time series:
curve1 = \
np.asarray([942.153,353.081,53.088,125.110,140.851,188.170,70.536,-122.473,-369.061,-407.945,88.734,484.334,267.762,65.831,74.010,-55.781,-260.024,-466.830,-524.511,-76.833,-36.779,-117.366,218.578,175.662,185.653,299.285,215.276,546.048,1210.132,3087.326,7052.849,13867.824,27156.939,51379.664,91908.266,148874.563,215825.031,290073.219,369567.781,437031.688])
The time values:
tvals = \
np.asarray([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40])
Using a numpy's function:
degree=10
legendrefit_curve1 = np.polynomial.legendre.Legendre.fit(tvals, curve1, deg=degree)
The fit seems pretty good:
# generate points of fitted curve
n=100
fitted_vals_curve1 = legendrefit_curve1.linspace(n=n)
# plot data and fitted curve
plt.scatter(tvals, curve1)
plt.plot(fitted_vals_curve1[0],fitted_vals_curve1[1],c='r')
What's the question
print(legendrefit_curve1)
returns:
leg([ 36823.85778316 96929.13731379 123557.55165344 112110.13559758
75345.0434688 32377.19460001 -182.38440131 -15562.47475287
-16142.22533582 -8379.06875482 -744.73929814])
However, I am using a Jupyter notebook, so if I just write legendrefit_curve1
, without print(), I get an output:
(What difference print() makes to Jupyter's output is related to this question.)
Clearly, print(legendrefit_curve1)
only gave the coefficients of each Legendre polynomial (same with legendrefit_curve1.coef
).
How do I get the values which transform x to be the argument of each Legendre polynomial?
ie how to obtain the values from the expression: -1.0512820512820513+0.05128205128205128x
: -1.0512820512820513
and 0.05128205128205128
(without just copying them manually)?
What didn't work
Relying on this thread I run:
for attr in dir(legendrefit_curve1):
print('###'+attr+'###')
print(getattr(legendrefit_curve1, attr))
This had a long text output, but I did not find -1.05
in it (ctrl-f
), so that suggest that the -1.0512820512820513
value did not get returned, so this method doesn't work.
回答1:
By looking at those numbers I realized I can construct them from math.
1/(len(curve1)-1)*2
, ie 1/39*2
returns: 0.05128205128205128
1+1/(len(curve1)-1)*2
ie 1+1/39*2
returns: `1.05
Which are the numbers we were looking for.
I still don't know how it is displayed when executing legendrefit_curve1
in a Jupyter Notebook cell, but that is less of the point.
I don't know why the formula above works, it'll probably be a question on math.stackexchange.com.
来源:https://stackoverflow.com/questions/63120942/how-do-i-get-the-function-which-transforms-an-input-to-be-the-argument-of-a-lege