PEST

PEST is a nonlinear parameter estimation and optimization package with a difference! The difference is that PEST can be used to estimate parameters for just about any existing model whether or not you have the model's source code. PEST is able to "take control" of a model, running it as many times as it needs while adjusting its parameters until the discrepancies between selected model outputs and a complementary set of field or laboratory measurements is reduced to a minimum in the weighted least-squares sense.

This model is public domain and can be downloaded for FREE using the link below.

For a model-independent graphical interface to PEST, see: GMS or Groundwater Vistas