Now assume that the model simplifies to x_{it} = \lambda_i f_t + e_{it} for t = 1,2...,T ; I =1, ..., N; but now the researcher has N = 200 and T = 200. We start x_{it} and write the generalized version of the factor model as: X_t = \Lambda F_t + e_t, ~~ t = 1,2,.., T and further assume that var(e_t) = \sum_{ee} which is a full (non-diagonal) matrix. How should the researcher estimate the model's parameters