Constant BABYBEAR_POSEIDON2_PARTIAL_ROUNDS_16 

pub const BABYBEAR_POSEIDON2_PARTIAL_ROUNDS_16: usize = 13;

Number of partial rounds for BabyBear Poseidon2 (width 16).

Derived from the Gröbner basis bound in the Poseidon2 paper (Eq. 1, R_GB term 3):

R_GB ≥ t − 7 + log_α(2) · min{κ/(t+1), log_2(p)/2} = 9 + 0.3562 · min{7.53, 15.5} = 11.682

With the +7.5% security margin: ⌈1.075 × 11.682⌉ = 13.