An additional independent model variable, e.g. defining a concentration , may be introduced. Switching points may be inserted where the integration is restarted to allow e.g. non-continous model changes. Switching points may become optimization parameters. Model functions may be defined by their Laplace transforms. The backtransformation is performed internally.
Some alternative methods based on direct search 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. Consistent initial values for index 1 formulations are computed internally. The approach is called the method of lines, i.e. the PDE is transformed into a system of ordinary differential equations.