How do I get “ranges” and other sensitivity analyses?

AMPL’s suffix feature can be used by solvers to return ranging information. See in particular the discussion of solver-defined suffixes in Section 14.3 of the AMPL book for an example of range output from CPLEX. The option listings for the CPLEX and Gurobi solvers contain more information about how to request and retrieve this information.

AMPL does not currently support “parametric” algorithms for postoptimal analysis of objective functions or constraint right-hand sides.

In practice, ranging often provides sensitivity information of limited usefulness, and parametric algorithms are limited to certain kinds of linear changes to the data. You may do better to write a simple AMPL script that solves the same model for a series of different parameter values. For an example, see the simple sensitivity analysis script developed in Section 13.1 of the AMPL book.