Model (conditional on working quantities): $$z_{\mathrm{work}} = X\beta + Z\eta + e,\qquad e \sim N(0, W^{-1})$$ $$\eta \sim N(0, \tau^2 I_q)$$
glmmfe_lmm_inner_fit(
z_work,
w_num,
X,
Z,
tau2,
approx = c("RSPL", "MSPL"),
vc_eps = 1e-12,
ridge_init = 1e-08
)where \(W = \mathrm{diag}(w_{\mathrm{num}})\).
Returns beta, eta and covariance blocks needed by RSPL/MSPL updates.
Does NOT form \(n \times n\) matrices.