Overview
The mean frontier plots out the set of achievable mean-variance, with the boundary of the set representing the minimum variance achievable for each target return.
Frontier
Graph showing the minimum variance set. The top portion is the efficient frontier. Returns are plotted on the y-axis, and variance is plotted on the x-axis.
Two Fund Theorem
Any point on the minimum variance set can be achieved by combining any two other funds in the set. That is, one can choose two points on the minimum variance set, and can then reach any point in the set by an appropriate combination of the two portfolios.