Numerical algorithms are implemented as stand-alone executable files and can be used also outside of the database. Salford FTN77, Absoft Pro Fortran, or Lahey F77 are attached. EASY-FIT comes with a full context sensitive help option and a handbook of about 320 pages that describes also the mathematical background. EASY-FIT generates plots by its own graphics routines in 2D and 3D format. In the latter case views can be adapted interactively.
Some alternative methods based on direct search and combinations are also available.
Systems of nonlinear equations are solved by stabilized Newton method. Ordinary differential equations are integrated by a couple of explicit and implicit codes, also with internal numerical differentiation. Differential algebraic equations can be solved up to index 3. Parameter estimation problems based on unstable differential equations can be solved by the shooting method. In case of a Laplace formulation of the model functions, the back-transformation is performed internally.