Sum of diagonal entries of a square matrix; equivalently Σ eigenvalues. Basis-independent, linear, and satisfies tr(AB)=tr(BA); is the sole (up to scalar) linear functional invariant under conjugation.
Sum of diagonal entries of a square matrix; equivalently Σ eigenvalues. Basis-independent, linear, and satisfies tr(AB)=tr(BA); is the sole (up to scalar) linear functional invariant under conjugation.