title: Trying to fit a sine function to phased light curve
body: <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  from lmfit import Model,Parameters
  
  
  f2= "KELT_N16_lc_006261_V01_west_tfa.dat"    
  t2="TIMES"   # file name
  
  NewData2 = np.loadtxt(t2, dtype=float, unpack=True)
  NewData = np.loadtxt(f2,dtype=float, unpack=True, usecols=(1,))
  
  flux = NewData   
  time= NewData2
  
  new_flux=np.hstack([flux,flux])
  
  # fold
  period = 2.0232               # period (must be known already!)
  
  foldTimes = ((time)/ period)  # divide by period to convert to phase
  foldTimes = foldTimes % 1   # take fractional part of phase only (i.e. discard whole number part)
  
  
  new_phase=np.hstack([foldTimes+1,foldTimes])
  
  print len(new_flux)
  print len(new_phase)
  
  
  def Wave(x, new_flux,new_phase):
      wave = new_flux*np.sin(new_phase+x)
      return wave
  model = Model(Wave)
  print "Independent Vars:", model.independent_vars
  print "Parameters:",model.param_names
  p = Parameters()
  p.add_many(('new_flux',13.42, True, None, None, None) )   
  p.add_many(('new_phase',0,True, None, None, None) )   
  
  result=model.fit(new_flux,x=new_phase,params=p,weights= None)
  
  
  plt.scatter(new_phase,new_flux,marker='o',edgecolors='none',color='blue',s=5.0, label="Period: 2.0232  days")   
  plt.ylim([13.42,13.54])
  plt.xlim(0,2)
  plt.gca().invert_yaxis()
  plt.title('HD 240121 Light Curve with BJD Correction')
  plt.ylabel('KELT Instrumental Magnitude')
  plt.xlabel('Phase')
  legend = plt.legend(loc='lower right', shadow=True)
  plt.scatter(new_phase,result.best_fit,label="One Oscillation Fit", color='red',s=60.0)
  plt.savefig('NewEpoch.png')
  print result.fit_report()
  </code></pre>
  
  <p>I am trying to fit a sine function to phased light curve data for a research project. However, I am unsure as to where I am going wrong, and I believe it lays in my parameters. It appears that the fit has an amplitude that is too high, and a period that is too long. Any help would be appreciated. Thank you!</p>
  
  <p>This is what the graph looks like now (Attempt at fitting a sine function to my dataset):</p>
  
  <p><img src="https://i.stack.imgur.com/SQsWT.png" alt="img"> </p>