title: Plotting line through scatter plot in xlsx writer
body: <p>Here's a scatter plot :</p>
  
  <p><a href="https://i.stack.imgur.com/xpgSU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xpgSU.png" alt="enter image description here"></a></p>
  
  <p>All Im trying to do is simply add a line through the point -.8 (y axis) , to .4 (x axis) , which crosses trough (0,0), but this is what I end up getting: </p>
  
  <p><a href="https://i.stack.imgur.com/2faV5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2faV5.png" alt="enter image description here"></a></p>
  
  <p>Here's my code:</p>
  
  <pre><code>diagonal = workbook.add_chart({'type':'line'})
  
  ###for line 
  worksheet.write(0,0,-.8)
  worksheet.write(1,0,.4) 
  
  ###net and gain are just excel columns  (for scatterplot)
  diagonal.add_series({'values':['sheet',0,0,1,0],'categories':net)
  scatter = workbook.add_chart({'type':'scatter'})
  scatter.add_series({'values':gain,'categories':net)
  
  diagonal.combine(scatter)
  worksheet.insert_chart(1,1,diagonal) 
  </code></pre>