Constant M_INT_DIAG_HZN 

pub const M_INT_DIAG_HZN: &[Elem];

Standardizing on the same coefficients as https://github.com/HorizenLabs/poseidon2.git (as used in its plain implementation of Poseidon2 for BabyBear)

These parameters are have been confirmed to pass the algorithms given in Grassi, Rechberger, and Schofnegger’s paper “Proving Resistance Against Infinitely Long Subspace Trails: How to Choose the Linear Layer” by running a version of the code provided with the paper adapted to include these parameters in what’s tested.

The full matrix can be constructed by as follows:

• Initialize a matrix with all 1s.
• Add these values along the diagonal.