rugarch roll plot. why abs(mu) in plot?

An HTML attachment was scrubbed...
URL: <https://stat.ethz.ch/pipermail/r-sig-finance/attachments/20181201/fdf5267d/attachment.html>

-------------- next part --------------
A non-text attachment was scrubbed...
Name: series_plot.png
Type: image/png
Size: 6747 bytes
Desc: not available
URL: <https://stat.ethz.ch/pipermail/r-sig-finance/attachments/20181201/fdf5267d/attachment.png>