title: How to put greek letters in latex knitr figure caption?
body: <p>I searched for this, but wasn't able to find it. In a knitr document, I want to put $\alpha_1$ as the caption to a plot like so:</p>
  
  <pre><code>&lt;&lt;fig.cap='$\alpha_1$'&gt;&gt;=
   plot(1:5,1:5)
  @
  </code></pre>
  
  <p>Trying to knit this comes back with the error</p>
  
  <pre><code>! Text line contains an invalid character.
  l.172 ...axwidth]{figure/plotSigma1} \caption[$^^G
                                                lpha_1$]{$^^Glpha_1$\label...
  </code></pre>
  
  <p>Is there a way?</p>