title: Overfitting with curve.fit
body: <p>can anyone help me struggle with fitting issue from curve.fit. I would like to fit my data to a second order equation. But I obtained a result like a linear equation.<a href="https://i.stack.imgur.com/rhwEn.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rhwEn.png" alt="enter image description here" /></a>
  Here is my code:</p>
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  from scipy.optimize import curve_fit
  
  def func(x, a, b, c):
      f = a*np.power(x, 2) + b*x + c
      return f
  
  xdata_prime=[3.0328562996216282, 3.101784841139168, 3.1707134502066894, 3.2396419917242292, 3.308570533241769, 3.3774990747593088, 3.3774990747593088, 3.4337789932367149, 3.4900589392912855, 3.5463388577686916, 3.6026187762460977, 3.6588987223006684]
  ydata_prime=[6.344300000000002, 6.723900000000002, 7.080399999999999, 7.399800000000001, 7.649099999999999, 7.753100000000002, 7.753100000000002, 7.658600000000002, 7.442100000000002, 7.180100000000001, 6.902700000000001, 6.6211]
  
  plt.plot(xdata_prime, ydata_prime, 'b-', label='data')
  popt, pcov = curve_fit(func, xdata_prime, ydata_prime)
  popt
  plt.plot(xdata_prime, func(xdata_prime, *popt), 'r-',label='fit')
  plt.xlabel('x')
  plt.ylabel('y')
  plt.legend()
  plt.show()
  </code></pre>