A direct consequence of EM is that the final solution
is constrained to be positive, complying with the assumption
that activity cannot physically have a negative
value. This further serves to provide a stable result, unlike
other algorithms where negative values are permitted.
Some care needs to be taken when using acceleration
techniques such as OS, since the degree of acceleration
may provide a solution after a single iteration which appears
noisy, since the algorithm has already reached a point equivalent to many EM iterations. This can be avoided by using a larger subset size so that the degree
of acceleration is reduced, but the stopping point is
maintained at that equivalent to a smaller number of EM
iterations.