This updates the ETA initial estimates based on the knowledge of d(eta)/d(theta)
rxUpdateEtas(DnDhS, DhS, initS, acceptNS)
This is the d(eta)/d(theta) list where there is a d(eta)/d(theta) matrix for each subject
This is the change in theta observed between steps.
This is the ETA initial condition matrix
Acceptance criteria for the new eta. |eta| < acceptNS for the new eta to be accepted.