Myra Saefong & Barbara Kollmeyer, MarketWatch ‘Alarm bell’ goes off over U.S. oil supply. Oil settled with a modest loss Thursday, following sharp declines in the prior session, as data showing that the global market remains awash in surplus oil, rising U.S. crude production and weak domestic gasoline demand kept pressure on prices. Natural-gas futures, Learn why Heather Bellini of Goldman Sachs Research sees virtual and augmented reality as the next computing platform. Watch Video It is possible for a tetrachoric correlation matrix to not be positive definite. Knol and Berger (1991) suggest that, with ML or Generalized (Weighted) least-squares (GLS/WLS) estimation of the common factor model, if the matrix is indefinite or ill-conditioned with respect to inversion, a smoothing procedure is required; they also describe a procedure for this.