

   CCaallccuullaattee VVaarriiaannccee--CCoovvaarriiaannccee MMaattrriixx ffoorr aa FFiitttteedd MMooddeell
   OObbjjeecctt

        vcov(x, ...)

   AArrgguummeennttss::

          x: a fitted model object.

        ...: additional arguments for method functions.

   DDeessccrriippttiioonn::

        Returns the variance-covariance matrix.  This is a
        generic function.  Functions with names beginning in
        `vcov.' will be methods for this function.  `lm',
        `glm', `nls'.

   VVaalluuee::

        a matrix of the estimated covariances between the
        parameter estimates in the linear or non-linear predic-
        tor of the model.

   SSeeee AAllssoo::

        `vcov.nlregb'

