A cyclic vector for a specified bounded linear operator 
on a Hilbert space 
is a vector 
for which the vector space
span of the orbit
 |
is dense in 
. In this case, the linear operator 
is said to be a cyclic
operator.
More generally, a vector 
is cyclic for an operator
algebra 
acting on a Hilbert space 
if 
is dense in 
. This is the sense used in the Reeh-Schlieder
theorem (Strohmaier et al. 2002).
