Register how a non-block Omega zero is parameterized
Source:R/rxSymInv.R
dot-rxSymInvBlockZeroFreeCallback.RdAn off-diagonal zero that does not split Omega into contiguous blocks is
not a zero of chol(Omega^-1), so it can be a free parameter (#1365).
rxSymInvCholCreate() only does that when a registered callback says so;
with no callback it errors as it always has. This is a compatibility hook
for nlmixr2est, not a user setting: the released nlmixr2est infers its own
omega parameter positions from the zero pattern of the matrix it passes in,
and accepting that matrix rather than its filled replacement makes
est="vae" stop with a position-count mismatch.