pub fn expand_a<P: Params>(rho: &[u8; 32]) -> [[[i32; 256]; 7]; 8]Expand description
Expand the public matrix A in NTT domain from a seed.
Implements Algorithm 32 of FIPS 204 (ExpandA). Generates a k-by-l matrix
of NTT-domain polynomials by calling rej_ntt_poly for each entry
with indices (s, r).
rho: 32-byte public seed (part of the public key).
Returns the matrix A-hat as a [[[i32; N]; MAX_L]; MAX_K] with valid
entries in rows 0..k and columns 0..l.