title: curve fitting with lmfit python
body: <p>I am new to python and trying to fit data using lmfit.  I am following on the lmfit tutorial here:
  <a href="http://lmfit.github.io/lmfit-py/parameters.html" rel="nofollow">http://lmfit.github.io/lmfit-py/parameters.html</a>
   and this is my code (based on the code explained in the above link):    </p>
  
  <pre><code>import numpy as np
  import lmfit 
  import matplotlib.pyplot as plt
  from numpy import exp, sqrt, pi
  from lmfit import minimize,Parameters,Parameter,report_fit
  
  data=np.genfromtxt('test.txt',delimiter=',')
  
  x=data[:,][:,0]
  y=data[:,][:,1]
  
  def fcn2fit(params,x,y):
      """model decaying sine wave, subtract data"""
      S1=params['S1'].value
      t0=params['t0'].value
      T1=params['T1'].value
      S2=params['S2'].value
      T2=params['T2'].value
  
      model = 1-(1-S1)*exp(-(x-t0)/T1)+S2*(1-exp(-(x-t0)/T2)
      return model - y  
  
  params = Parameters()
  params.add('S1', value=0.85, min=0.8, max=0.9)
  params.add('t0', value=0.05, min=0.01, max=0.1)
  params.add('T1', value=0.2, min=0.1, max=0.3)
  params.add('S2', value=0.03, min=0.01, max=0.05)
  params.add('T2', value=0.3, min=0.2, max=0.4)
  
  result = minimize(fcn2fit, params, args=(x,y))
  final = y + result.residual
  
  report_fit (params)
  
  try:
      import pylab
      pylab.plot(x,y, 'k+')
      pylab.plot(x,final, 'r')
      pylab.show()
  except:
      pass
  </code></pre>
  
  <p>Problem:
  it return syntax error for line return model-y</p>
  
  <p>I appreciate if you could please let me to right direction.</p>