Allow short selling in portopt

In Finanical toolbox,the Portopt funtion set the default value 
of minimum weights equals 0. But I want to draw a efficient 
frontier based on a portfolio consists of 3 assets which the 
short selling is allowed. Which values do I have to change to 
get this done? Or which other functions do I have to use?
Thanks in advance.

Answer 1

[owr]

Check out the function portcons and the "AssetLims" parameter.