Post #122

Let F \in su(D) be fixed Hermitian. There exist integers m <= D and Hermitian involutions {(Q_j, K_j)} (j \in [1,m]) with real scalars (a_j, b_j, c_j) such that F = \sum_j a_j Q_j + b_j K_j Q_j K_j + i c_j [K_j, Q_j]). In the worst case m~\Omega(D). With D=2^n, exponential involutions are needed. -- guru JK's wisdom