This document explains the definition of a mathematical model supposed to
be recognized by Flint.

A model has an arbitrary number of variables, each of which belongs to one of
two groups: independent and dependent ones.

A variable has its name and the set of its possible values, called its domain.
Note that the domain determines its dimension.

A given model is defined by a set of equations constraining the values of dependent
variables in terms of all of variables.  Equations can have parameters, which are
like variables, but do not come together with any equations defining them.

Although equations in a model can be of any form in principle, typical classes
of them are:
- algebraic equations,
- difference equations,
- ordinary differential equations,
- delay differential equations, and
- stochastic differential equations.

Some of equations are effective only when independent variables take specific
values.  For example, an initial condition is represented by such equations.


Add memo on mathematical models
Add memo on mathematical models
