A Matrix Approach to the Rational Invariants of Certain Classical Groups   over Finite Fields of Characteristic Two
  Let ${\mathbb F}_q$ be a finite field of characteristic two and ${\mathbb F}_q(X_1,...,X_n)$ a rational function field. We use matrix methods to obtain explicit transcendental bases of the invariant subfields of orthogonal groups and pseudo-symplectic groups on ${\mathbb F}_q(X_1,...,X_n)$ over ${\mathbb F}_q$. 
Zhongming Tang, Zhe-xian Wan