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.