title: Warning: set it to a single string instead
body: <p>What does this warning mean? How can I get rid of this?</p>
  <pre><code>Support for setting the 'text.latex.preamble' or 'pgf.preamble' rcParam to a list of strings is deprecated since 3.3 and will be removed two minor releases later; set it to a single string instead.
    plt.rcParams['text.latex.preamble'] = [r&quot;\usepackage{bm}&quot;, [r&quot;\usepackage{amsmath}&quot;]
  </code></pre>
  <p>Code:</p>
  <pre><code>import matplotlib.pyplot as plt
  plt.rcParams['text.latex.preamble'] = [r&quot;\usepackage{bm}&quot;], [r&quot;\usepackage{amsmath}&quot;]
  
  params = {'text.usetex' : True,
            'font.size' : 28,
            'font.family' : 'lmodern',
            }
  plt.rcParams.update(params)
  </code></pre>