“…where M = C n×n . In recent years there has been substantial interest in structured pseudospectra [KKK10, Kar11,Ru06], where A is in some linear subspace M ⊂ C n×n and the perturbed matrices B in (1.1) are restricted to lie in the same subspace M. Cases of particular interest include M = R n×n (real pseudospectra [BRQ98, GL13,Ru06]) and M = Ham(n), the space of complex or real Hamiltonian matrices (Hamiltonian pseudospectra [ABKMM11,GKL13]). There are, however, also structures of interest where M ⊂ C n×n is not a linear space, but a matrix Lie group or, more generally, a matrix manifold.…”