Coherent risk measure
A coherent risk measure satifies the following features:
- sub-additivity: ρ(R1 + R2) ≤ ρ(R1) + ρ(R2)
- monotonicity: ρ(R1) ≥ ρ(R2) if R1 ≥ R2
- positive homogeneity: βρ(R) = ρ(βR), for all β>0.
- translation invariant: ρ(R) + c = ρ(c + R) for all constants c.
Beware! the VAR measure violates the first feature (sub-additivity).