title: Mathematical expression in axis label
body: <p>In R, I use <code>expression(theta[l])</code> so that the label of my plot axis is that same as <code>$\theta_l$</code> from LaTeX. For esthetic reasons, I'd rather like to display <code>$\theta_\ell$</code>. Can you help me?</p>
  
  <p><img src="https://i.stack.imgur.com/4qHwX.gif" alt="enter image description here"></p>
  
  <hr>
  
  <p><strong>EDIT</strong></p>
  
  <p>Before, I did</p>
  
  <pre><code>plot(1:10, 1:10, xlab=expression(theta[l]))
  </code></pre>
  
  <p>and I exported the resulting picture in pdf. Then, using</p>
  
  <pre><code>\begin{figure}[htbp]
  \centerline{\includegraphics[scale=.6]{test.pdf}}
  \end{figure}
  </code></pre>
  
  <p>my picture was inserted in LaTeX.</p>
  
  <p>Following the comments, here is what I now do:</p>
  
  <pre><code>require(tikzDevice)
  tikz("test.tex", standAlone=TRUE, width=5, height=5)
  
  plot(1:10, 1:10, xlab="$\\theta_\\ell$")
  
  dev.off()
  tools::texi2pdf('test.tex')
  system(paste(getOption('pdfviewer'),'test.pdf'))
  </code></pre>
  
  <p>However, when I insert the resuling plot in LaTeX, the quality of the figure is not as good as before. Is there something more that I can do?</p>