Portfolio Allocation while shorting stocks

Hi all,

If I want to have constraints for assets so that I can only short them and then the sum of total allocation should be -1, how to achieve it in Matlab?

While using pcalims, I can only choose each asset minimum and maximum value, but not the sum of allocation as "-1". While using pcpval, I can choose total portfolio allocation as -1, but then it always becomes an unbounded and hence unsolved problem.

What am I missing when I want to have the aforesaid two constraints. Really appreciate the help.