2 HESSE
  Syntax: HESSE

  Recalculates the covariance  matrix. This is very useful if the errors
  get too small for some reason.

  Note that when the  matrix gets printed the  off-diagonal elements are
  the correlation coefficients, not the elements of the matrix:

  C(i,j) = V(i,j) / sqrt(V(i,i)*V(j,j)).

  The diagonal elements are the parabolic errors.

  If the `PRINTOUT' level is 0 or greater the covariance matrix is
  also shown.

