title: Having trouble while using scipy.integrate.odeint with python
body: <p>I was trying to use odeint to solve a problem. My code is as below:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  from scipy.integrate import odeint
  
  eta=1.24e-9/2
  def fun(x):
      f=1.05e-8*eta*x**(1.5)*np.exp(13.6/x)
      return (np.sqrt(1.+4*f)-1)/2./f
  x=np.arange(0,1,0.001)
  y=odeint(fun,x,0)[0]
  plt.plot(x,y)
  plt.plot(x,x)
  plt.show()
  </code></pre>
  
  <p>It the two curves are the same, which is obviously wrong. If I plot the function, it will looks like a step function, which is very very small before about 0.3 and exponentially goes to 1. Can you help me figure out what's wrong with it? Thank you!</p>