在Python中具有零斜率约束的曲线拟合
在Python中具有零斜率约束的曲线拟合
提问于 2019-04-16 02:40:51
我希望对以下数据进行曲线拟合，这样我就可以使其在边缘处的斜率为零的情况下拟合趋势。polyfit的输出将拟合该数据，但在边缘处的斜率不为零。
这是我想要输出的东西--请原谅我的粉刷工作。我需要像这样拟合它，这样我才能正确地去除数据的正弦/余弦偏差，这些偏差不是真实的，朝向中心。
以下是数据：
[0.23353535 0.25586247 0.26661164 0.26410896 0.24963951 0.22670266
0.19955422 0.17190263 0.1598439 0.17351905 0.18212444 0.18438673
0.17952432 0.18314894 0.19265689 0.19432385 0.19605163 0.20326011
0.20890851 0.20590997 0.21856518 0.23771665 0.24530019 0.23940831
0.22078396 0.23075128 0.2346082 0.22466281 0.24384843 0.26339594
0.26414153 0.24664183 0.24278978 0.31023648 0.3614195 0.37773436
0.3505998 0.28893167 0.23965877 0.24063917 0.27922502 0.32716477
0.36553767 0.42293146 0.50968856 0.5458872 0.52192533 0.45243764
0.36313155 0.3683921 0.40942553 0.4420537 0.46145585 0.4648034
0.4523771 0.4272876 0.39404616 0.3570107 0.35060245 0.3860975
0.3996996 0.44551122 0.46611032 0.45998383 0.4309985 0.38563925
0.37105605 0.4074444 0.48815584 0.5704579 0.6448988 0.7018853
0.73397845 0.73739105 0.7122451 0.6618154 0.591451 0.5076601
0.48578677 0.47347385 0.4791471 0.48306277 0.47025493 0.43479836
0.44380915 0.45868078 0.5341566 0.57549906 0.55790776 0.56244135
0.57668275 0.561856 0.67564166 0.7512851 0.76957643 0.7266262
0.734133 0.7231936 0.6776926 0.60511285 0.51599765 0.5579323
0.56723005 0.5440337 0.5775593 0.5950776 0.5722321 0.57858473
0.5652703 0.54723704 0.59561515 0.7071321 0.8169259 0.91443264
0.9883759 1.0275097 1.0235045 0.9737119 1.029139 1.1354861
1.1910824 1.1826864 1.1092159 0.9832138 0.9643041 0.92324203
0.9093703 0.88915515 1.0007693 1.0542978 1.0857164 1.0211861
0.88474303 0.8458009 0.76522666 0.7478076 0.90081936 1.0690157
1.1569089 1.1493248 1.0622779 1.0327609 0.9805119 0.9583969
0.8973544 0.9543319 0.9777171 0.94951093 0.97323567 1.0244237
1.0569099 1.0951824 1.0771195 1.3078191 1.7212077 2.09409
2.320331 2.3279085 2.125451 1.7908521 1.4180487 1.0744424
1.0218129 1.0916439 1.1255138 1.125803 1.1139745 1.2187989
1.300092 1.3025533 1.2312403 1.221301 1.2535597 1.2298189
1.1458241 1.1012102 1.0889369 1.1558667 1.3051153 1.4143198
1.6345526 1.8093723 1.9037704 1.8961821 1.7866236 1.5958548
1.3865516 1.5308585 1.6140417 1.627337 1.5733193 1.4981418
1.5048542 1.4935548 1.4798748 1.4131776 1.3792214 1.3728334
1.3683671 1.3593615 1.2995907 1.2965002 1.366058 1.4795257
1.5462885 1.61591 1.5968509 1.5222199 1.6210756 1.7074443
1.8351102 2.3187535 2.6568012 2.7676315 2.6480794 2.3636303
2.0673316 1.9607923 1.8074365 1.713272 1.5893831 1.4734347
1.507817 1.5213271 1.6091452 1.7162323 1.7608733 1.7497622
1.9187828 2.0197518 2.0487514 2.01107 1.9193696 1.7904462
1.8558109 2.1955926 2.4700975 2.6562278 2.675197 2.6645825
2.6295316 2.4182043 2.2114453 2.2506614 2.2086055 2.0497518
1.9557768 1.901191 2.067513 2.1077373 2.0159333 1.8138607
1.5413624 1.600069 1.7631899 1.9541935 1.9340311 1.805134
2.0671906 2.2247658 2.2641945 2.3594956 2.2504601 1.9749025
1.8905054 2.0679731 2.1193469 2.0307171 2.0717037 2.0340347
1.925536 1.7820351 1.9467943 2.315468 2.4834185 2.3751369
2.0240622 1.9363666 2.1732547 2.3113241 2.3264208 2.22015
2.0187428 1.7619076 1.796859 1.8757095 2.0501778 2.44711
2.6179967 2.508112 2.1694388 1.7242104 1.7671669 1.862043
1.8392721 1.7120028 1.6650634 1.6319505 1.482931 1.5240219
1.5815579 1.5691646 1.4766116 1.3731087 1.4666644 1.4061015
1.3652745 1.425564 1.4006845 1.5000012 1.581379 1.6329607
1.6444355 1.6098644 1.5300899 1.6876912 1.8968476 2.048039
2.1006014 2.0271482 1.8300935 1.6986666 1.9628603 2.0521066
1.9337255 1.6407858 1.2583638 1.2110122 1.2476432 1.2360718
1.2886397 1.2862154 1.2343681 1.1458222 1.209224 1.2475786
1.2353342 1.1797879 1.0963987 1.0928186 1.1553882 1.1569618
1.1932304 1.3002363 1.3386917 1.2973225 1.1816871 1.0557054
0.9350373 0.896656 0.8565816 0.90168726 0.9897751 1.02342
1.0232298 1.1199353 1.1466643 1.1081418 1.0377598 1.0348651
1.0223045 1.0607077 1.0089502 0.885213 1.023178 1.1131796
1.1331098 1.0779471 0.9626393 0.81472665 0.85455835 0.87542623
0.87286425 0.89130884 0.9545931 1.0355722 1.0201533 0.93568784
0.9180018 0.8202782 0.7450139 0.72550577 0.68578506 0.6431666
0.66193295 0.6386373 0.7060119 0.7650972 0.80093855 0.803342
0.76590335 0.7151591 0.6946282 0.7136788 0.7714012 0.8022328
0.79840165 0.8543819 0.8586749 0.8028453 0.7383879 0.73423904
0.65107304 0.61139977 0.5940311 0.6151931 0.59349155 0.54995483
0.5837645 0.5891752 0.56406695 0.5638191 0.5762535 0.58305734
0.5830114 0.57470953 0.5568098 0.52852243 0.49031836 0.45275375
0.47168964 0.46634504 0.4600581 0.45332378 0.41508177 0.3834329
0.4137769 0.41392407 0.3824464 0.36310086 0.434278 0.48041886
0.49433306 0.475708 0.43060693 0.36886734 0.34740242 0.34108457
0.36160505 0.40907663 0.43613982 0.4394311 0.42070773 0.38575593
0.3827834 0.4338096 0.46581286 0.45669746 0.40830874 0.3505502
0.32584783 0.3381971 0.33949164 0.36409503 0.3759155 0.3610108
0.37174097 0.39990777 0.38925973 0.34376588 0.32478797 0.32705626
0.3228174 0.30941254 0.28542265 0.2687348 0.25517422 0.26127565
0.27331188 0.3028561 0.31277937 0.29953563 0.2660389 0.27051866
0.2913383 0.30363902 0.30684754 0.3011791 0.28737035 0.26648855
0.26413882 0.25501928 0.23947525 0.21937743 0.19659272 0.18965112
0.21511254 0.23329383 0.24157354 0.2391297 0.22697571 0.20739041
0.1855308 0.18856761 0.19565174 0.20542233 0.21473111 0.22244582
0.22726117 0.22789808 0.22336568 0.21322969 0.20314343 0.2031754
0.19738965 0.1959791 0.20284075 0.20859875 0.21363212 0.21804498
0.22160804 0.22381367]这很接近，但并不完全是因为边缘不是零斜率：How do I fit a sine curve to my data with pylab and numpy?
有没有什么方法可以让我不用编写自定义算法就能做到这一点呢？谢谢。
回答 2
Stack Overflow用户
发布于 2019-04-16 03:44:23
这是一个适合你的数据的洛伦兹类型的峰值方程，对于"x“值，我使用了一个类似于我在你的帖子中看到的示例输出图的索引。我还放大了峰值中心，以便更好地显示您提到的正弦形状。您可以从该峰值方程中减去预测值，以便在您讨论时对原始数据进行条件处理或预处理。
a = 1.7056067124682076E+02
b = 7.2900803359572393E+01
c = 2.5047064423525464E+02
d = 1.4184767800540945E+01
Offset = -2.4940994412221318E-01
y = a/ (b + pow((x-c)/d, 2.0)) + Offset
Stack Overflow用户
发布于 2019-04-23 23:19:57
从您自己的基于正弦拟合的示例开始，我添加了约束，使模型的导数在端点必须为零。我使用symfit实现了这一点，这是我编写的一个包，用来简化这类事情。如果您更喜欢使用scipy来完成此操作，您可以根据需要调整示例以适应该语法，symfit只是使用sympy添加符号操作的最小化程序的包装器。
# Make variables and parameters
x, y = variables('x, y')
a, b, c, d = parameters('a, b, c, d')
# Initial guesses
b.value = 1e-2
c.value = 100
# Create a model object
model = Model({y: a * sin(b * x + c) + d})
# Take the derivative and constrain the end-points to be equal to zero.
dydx = D(model[y], x).doit()
constraints = [Eq(dydx.subs(x, xdata[0]), 0),
Eq(dydx.subs(x, xdata[-1]), 0)]
# Do the fit!
fit = Fit(model, x=xdata, y=ydata, constraints=constraints)
fit_result = fit.execute()
print(fit_result)
plt.plot(xdata, ydata)
plt.plot(xdata, model(x=xdata, **fit_result.params).y)
plt.show()打印如下：(来自当前的symfit PR#221，它可以更好地报告结果。)
Parameter Value Standard Deviation
a 8.790393e-01 1.879788e-02
b 1.229586e-02 3.824249e-04
c 9.896017e+01 1.011472e-01
d 1.001717e+00 2.928506e-02
Status message Optimization terminated successfully.
Number of iterations 10
Objective <symfit.core.objectives.LeastSquares object at 0x0000016F670DF080>
Minimizer <symfit.core.minimizers.SLSQP object at 0x0000016F78057A58>
Goodness of fit qualifiers:
chi_squared 29.72125657199736
objective_value 14.86062828599868
r_squared 0.8695978050586373
Constraints:
--------------------
Question: a*b*cos(c) == 0?
Answer: 1.5904051811454707e-17
Question: a*b*cos(511*b + c) == 0?
Answer: -6.354261416082215e-17
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/55695428
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