  Many Lagrangians of physical theories can be expressed as eigenvalues of
certain, relatively simple, matrices involving Dirac gamma matrices. We give
concrete examples for Lagrangian corresponding to a point particle coupled to
electromagnetic field, electrodynamics, nonabelian gauge theories, extended
objects and gravity. We also discuss (in case of a point particle) what are the
implications of the least action principle applied to matrix Lagrangians.
