EASY-FIT is an interactive software system to identify parameters in explicit model functions, dynamic systems of equations, Laplace transformations, systems of ordinary differential equations, differential algebraic equations, or systems of one-dimensional time-dependent partial differential equations with or without algebraic equations. Proceeding from given experimental data, i.e. observation times and measurements, the minimum least squares distance of measured data from a fitting criterion is computed, that depends on the solution of the dynamic system. The model functions may depend also on an additional independent variable that could represent for example a concentration value of an experiment. The software system is implemented in form of a relational database under MS-Access 97 running under MS-Windows. The underlying numerical algorithms are coded in FORTRAN and are executable independently from the interface. Model functions are either interpreted and evaluated symbolically by a program called PCOMP, that allows in addition automatic differentiation of nonlinear model functions, or by user-provided FORTRAN subroutines. In the latter case interfaces for the Fortran compilers Watcom F77/386, Salford FTN77, Lahey F77L-EM/32 and Microsoft Fortran PowerStation are provided.

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