A partly experimental plot() method for
CLA() objects.
It draws the efficient frontier in the \(\mu_w,\sigma_w\) aka (mean,
std.dev.) plane.
Currently, this is quite rudimentary.
Future improvements would allow
- to add the/some single asset points,
- to correctly (`hyperbolically') interpolate between turning points
- add text about the number of (unique) critical points
- add option add = FALSE which when TRUE would use
lines instead plot.