MFIT /METHOD

      ANNEAL  Simulated annealing technique. This may require a  very  large
        number of function evaluation.
      POWELL  Gradient  using  the  Powell  method (see Press et al. for de-
        tails).
      SIMPLEX Classical Simplex amoeba search
      ROBUST  A combination of Simplex + Slatec, to be used with large  ini-
        tial steps.
      SLATEC  Modified  Levenberg  Marquardt  method with adaptive steps, as
        implement in the Slatec library.

    All methods require a proper choice of initial values and steps. The AN-
    NEAL method is much more robust against poor guesses, but may require 10
    to 100 times more function evaluations than any other.