i need to impose a constraint on the variance of my decision variables: x1, x2, x3 etc..

As the constraint becomes quadratic, i need to know how to linearize it. I will eventually solve it using LpSolve.

```
(x1 - Mean)^2 + (x2 - Mean)^2 + (x3 - Mean)^2 + (x4 - Mean)^2 <= 15
Mean = (x1+x2+x3+x4)/4
```