Numerical nonlinear algebra is applied to maximum likelihood estimation for
Gaussian models defined by linear constraints on the covariance matrix. We examine
the generic case as well as special models (e.g., Toeplitz, sparse, trees) that are of
interest in statistics. We study the maximum likelihood degree and its dual analogue,
and we introduce a new software package
LinearCovarianceModels.jl for solving
the score equations. All local maxima can thus be computed reliably. In
addition we identify several scenarios for which the estimator is a rational
function.
Keywords
linear covariance model, maximum likelihood, dual maximum
likelihood, numerical nonlinear algebra