log-likelihood Gaussian oblique factor structure correlation matrix with gradient for d variables and m groups,
oblique_grad_nllk(theta, grsize, Robs, nsize=100)negative log-likelihood and gradient for Gaussian p-factor model
vector of length d + m*(m-1)/2; d loading parameters followed by m*(m-1)/2 entries in correlation matrix of latent variables (lower triangle by row)
vector of group sizes (variables ordered by group)
dxd empirical correlation matrix
sample size if available