- A matrix m is negative semidefinite if Conjugate[x].m.x≤0 for all nonzero vectors x.
- NegativeSemidefiniteMatrixQ works for symbolic as well as numerical matrices.
- For approximate matrices, the option Tolerance->t can be used to indicate that all eigenvalues λ satisfying λ≤t λmax are taken to be zero where λmax is an eigenvalue largest in magnitude.
- The option Tolerance has Automatic as its default value.
Introduced in 2014