AMPL stands for "A Modeling Language for Mathematical Programming". It is used to describe mathematical programmes.
AMPL is a commerical software package from Bell Laboratories and is also
distributed by ILOG along with the mixed-integer linear programme solver CPLEX.
For more details see the main AMPL website:
www.ampl.com
and there is a good, fairly comprehensive book on AMPL:
AMPL: A Modeling Language for Mathematical Programming
However, you don't need to pay for AMPL right away! There is a limited functionality student version
which also provides CPLEX (the mixed-integer linear programme solver from ILOG)
and MINOS (the nonlinear programme solver from the
Systems Optimization Laboratory at Stanford University). This Student Version
will have enough functionality for the many of the problems you will encounter in the case studies on the OpsRes Web.
You can also use AMPL over the web at the AMPL website's web interface or you can use AMPL as an interface to many diferent
optimisation solvers at the NEOS Server for Optimization.