Notes on Hermitian Matrices and Vector Spaces 1. Hermitian matrices Defn: The Hermitian conjugate of a matrix is the transpose of its complex conjugate. So, for example, if M= 0 @ 1 i 0 2 1 i 1 + i 1 A; then its Hermitian conjugate Myis My= 1 0 1 + i i 2 1 i : In terms of matrix elements, [My] ij = ([M] ji): Note that for any matrix (Ay)y= A:

Traceless Matrices that are not Commutators Thesis directed by Associate Professor of Mathematics, Dr. Zachary Mesyan ABSTRACT. By a classical result, for any ﬁeld F and a positive integer n, a matrix in M n(F) is a commutator if only and if it has trace zero. This is no longer true if F is replaced with an arbitrary ring R. This gives, in particular, a strong negative solution to the problem whether n × n traceless matrices are necessarily commutators over a commutative base ring, for any n ≥ 2. Keywords: matrix rings , commutators , generalized commutators , traceless matrices , elementary divisor rings This gives, in particular, a strong negative solution to the problem whether n × n traceless matrices are necessarily commutators over a commutative base ring, for any n ≥ 2. Do you want to matrices X and Y ( not determined uniquely by Z ); then Trace(Z) := ∑ i z ii = 0 because Trace(XY) = Trace(YX) for all matrices X and Y both of whose products XY and YX are square. Conversely, according to an unobvious old theorem, if Trace(Z) = 0 then Z must be a commutator. Mar 31, 2016 · is traceless, and (by Theorem 2) every traceless matrix is a sum of three nilpotent matrices. However, despite the fact that the characteristic of Z is 0, there are traceless 2 × 2 matrices over

## Properties of 2x2 Hermitian matrices. Themostgeneralsuchmatrixcanbe described1 H = h 0 +h 3 h 1 −ih 2 h 1 +ih 2 h 0 − h 3 (1) traceless,Hermitianandhasdet

Mar 31, 2016 · is traceless, and (by Theorem 2) every traceless matrix is a sum of three nilpotent matrices. However, despite the fact that the characteristic of Z is 0, there are traceless 2 × 2 matrices over \$\begingroup\$ The paper of Rosset and Rosset contains an explicit calculation for 2x2 matrices over a PID. The math review, and to some extent the paper, claim that it solves this for general square matrices over PIDs, but I do not see that this is the case. \$\endgroup\$ – Jack Schmidt Apr 18 '10 at 17:48 I'll assume a square matrix with real entries in my answer. 1) A matrix with trace zero has both positive and negative eigenvalues, except if the matrix is the zero matrix.

### with a traceless hermitian matrix L. It is conveniently expressed as a linear combination L = ~L ·~Λ ≡ NX2−1 j=1 L jΛ j, L j ∈ R, (8) with the set ~Λ forming a basis for traceless hermitian matrices, Λ j † = Λ j, called the generators. At the same time, they are a basis of the Lie algebra su(N) of SU(N), satisfying the commutation

Mar 31, 2016 · is traceless, and (by Theorem 2) every traceless matrix is a sum of three nilpotent matrices. However, despite the fact that the characteristic of Z is 0, there are traceless 2 × 2 matrices over \$\begingroup\$ The paper of Rosset and Rosset contains an explicit calculation for 2x2 matrices over a PID. The math review, and to some extent the paper, claim that it solves this for general square matrices over PIDs, but I do not see that this is the case. \$\endgroup\$ – Jack Schmidt Apr 18 '10 at 17:48 I'll assume a square matrix with real entries in my answer. 1) A matrix with trace zero has both positive and negative eigenvalues, except if the matrix is the zero matrix.