title: lmfit VoigtModel eval() keeps giving exact same values for different parameters set?
body: <p>I have a quick question regarding the <code>eval()</code> function for the VoigtModel. I have a few different parameters sets and am trying to evaluate under a set of x values. A simple demonstration is down below. Somehow, no matter what parameter set I use, the <code>eval()</code> keeps giving me the same values.</p>
  <pre><code>from lmfit.models import VoigtModel
  import numpy as np
  import matplotlib.pyplot as plt
  
  p1={'v0_amplitude': 0.7895507911965995, 'v0_center': 0, 'v0_sigma': 0.3115195639177176, 'v0_gamma': 0.3115195639177176}
  p2={'v1_amplitude': 0.2433671058552931, 'v1_center': 0, 'v1_sigma': 0.5154224820790644, 'v1_gamma': -0.10060349484692119}
  p3={'v2_amplitude': 0.2560477563760484, 'v2_center': 0, 'v2_sigma': 0.19387399410496087, 'v2_gamma': 0.5953440400428517}
  
  p=[p1, p2, p3]
  v1=VoigtModel(prefix='v0_')
  v2=VoigtModel(prefix='v1_')
  v3=VoigtModel(prefix='v2_')
  
  v = [v1, v2, v3]
  x = np.linspace(-10,10, 100)
  
  for i in range(3):
    y = v[i].eval(p[i], x=x)
    plt.plot(x, y)
  plt.show()
  </code></pre>
  <p>what it gives me is exactly three overlapped profiles <a href="https://i.stack.imgur.com/aJjrN.png" rel="nofollow noreferrer">figure of three overlapping lineshapes</a>. However, obviously, they all should be different. I am not sure where it really goes wrong. Any help maybe?</p>