Constant ERR_COEFF_4 

pub const ERR_COEFF_4: f64 = _; // 2.664535259100382E-15f64

Absolute error coefficient for Matrix::<4>::det_direct.

For any 4×4 matrix A with finite f64 entries,

|A.det_direct() - det_exact(A)|  ≤  ERR_COEFF_4 · p(|A|)

where p(|A|) is the absolute Leibniz sum. det_direct for D=4 hoists six 2×2 minors, combines them into four 3×3 cofactors, then reduces those with an FMA row combination, yielding the 12·EPS + 128·EPS² bound. See REFERENCES.md [8] for the Shewchuk framework these bounds follow.

Prefer Matrix::det_errbound over this constant for typical use; see ERR_COEFF_2 for a worked example.