Published online by Cambridge University Press: 30 May 2018
Fix a finite semigroup $S$ and let
$a_{1},\ldots ,a_{k},b$ be tuples in a direct power
$S^{n}$. The subpower membership problem (SMP) for
$S$ asks whether
$b$ can be generated by
$a_{1},\ldots ,a_{k}$. For combinatorial Rees matrix semigroups we establish a dichotomy result: if the corresponding matrix is of a certain form, then the SMP is in P; otherwise it is NP-complete. For combinatorial Rees matrix semigroups with adjoined identity, we obtain a trichotomy: the SMP is either in P, NP-complete, or PSPACE-complete. This result yields various semigroups with PSPACE-complete SMP including the six-element Brandt monoid, the full transformation semigroup on three or more letters, and semigroups of all
$n$ by
$n$ matrices over a field for
$n\geq 2$.
The author was supported by the Austrian Science Fund (FWF): P24285.