Sample fixed effect coefficients
betaBlock(Omega, R, theta, X, Z, p, A, N)
current covariance matrix
design matrix model parameters (differs per person)
design matrix for random effects (differs per person)
dimension X (number of columns/variables+indicator variables)
prior variance of fixed effect coefficients
sample size at second level
current outcome vector (Y.I=cos(theta)*R, Y.II=sin(theta)*R)