# Nonlinear Models#

The nonlinear model represents a general optimization problem with an objective function and/or constraints over variables of various types.

This model is especially suited for use with decision variables that represent a common logic, such as subsets of choices or permutations of ordering. For example, in a traveling salesperson problem permutations of the variables representing cities can signify the order of the route being optimized and in a knapsack problem the variables representing items can be divided into subsets of packed and not packed.

The `Model`

class encodes this model and
its methods provide convenient utilities for constructing such models.