title: Want to make a line, using a handle to a figure in MATLAB
body: <p>I have a problem, where I already have a handle to a figure created, and I want to somehow now draw a line, given that handle. For example, I have:</p>
  
  <pre><code>f1 = figure(1);
  a1 = gca;
  </code></pre>
  
  <p>For commands like <code>plot</code> and <code>surf</code>, I can pass the axes and/or figure handles to tell it to plot to that particular figure. However, how do you do this with the <code>line</code> command? There does not seem to be a way as far as I know... thank you.</p>