In algebraic statistics, the maximum likelihood degree of a statistical model is the
number of complex critical points of its log-likelihood function. A priori
knowledge of this number is useful for applying techniques of numerical algebraic
geometry to the maximum likelihood estimation problem. We compute the
maximum likelihood degree of a generic two-dimensional subspace of the space of
Gaussian
covariance matrices. We use the intersection theory of plane curves to show that this
number is
.
Keywords
algebraic geometry, algebraic statistics, linear Gaussian
covariance models, intersection theory, plane curves,
maximum likelihood estimation, maximum likelihood degree