Sample subject specific random effects
b.f(Omega, beta, Y, X, q, Z, ZtZ, N)current covariance matrix
current fixed effect coefficients vector
current outcome vector (Y.I=cos(theta)*R, Y.II=sin(theta)*R)
design matrix model parameters (differs per person)
dimension Z(number of random effects)
design matrix for random effects (differs per person)
transpose(Z)*Z
sample size at second level