Computes the exact frustration index of a signed network using linear programming

## Details

The frustration index indicates the minimum number of edges whose removal results in a balance
network. The function needs the following packages to be installed: `ompr`

, `ompr.roi`

,`ROI`

, and `ROI.plugin.glpk`

.
The function Implements the AND model in Aref et al., 2020

## References

Aref, Samin, Andrew J. Mason, and Mark C. Wilson. "Computing the line index of balance using linear programming optimisation." Optimization problems in graph theory. Springer, Cham, 2018. 65-84.

Aref, Samin, Andrew J. Mason, and Mark C. Wilson. "A modeling and computational study of the frustration index in signed networks." Networks 75.1 (2020): 95-110.