Matrix Trace -- from Wolfram MathWorld

Abstraction: Definition and properties of the matrix trace operation

Key points:

• Trace of an n x n matrix is the sum of its diagonal elements; implemented in Wolfram Language as Tr[list]
• In group theory, traces are known as group characters
• Trace is invariant under similarity transformation: Tr(B^-1 AB) = Tr(A)
• Tr(AB) = Tr(BA): trace of a product of two square matrices is independent of multiplication order
• For three or more matrices, trace is invariant only under cyclic permutations of order
• Product of a symmetric and antisymmetric matrix has zero trace

Connections: Matrix Trace · Linear Algebra · Wolfram Mathworld

Source: http://mathworld.wolfram.com/MatrixTrace.html