proprietary software maintained by AMPL Optimization LLC. However, several online services exist, providing free modeling and solving facilities using AMPL. A free student version with limited functionality and a free full-featured version for academic courses are also available. AMPL can be used from within Microsoft Excel via the SolverStudio Excel add-in. The AMPL Solver Library (ASL), which allows reading nl files and provides the automatic differentiation, is open-source. It is used in many solvers to implement AMPL connection. Status history This table present significant steps in AMPL history. A sample model A transportation problem from George Dantzig is used to provide a sample AMPL model. This problem finds the least cost shipping schedule that meets requirements at markets and supplies at factories. set Plants; set Markets; # Capacity of plant p in cases param Capacity{p in Plants}; # Demand at market m in cases param Demand{m in Markets}; # Distance in thousands of miles param Distance{Plants, Markets}; # Freight in dollars per case per thousand miles param Freight; # Transport cost in thousands of dollars per case param TransportCost{p in Plants, m in Markets} := Freight * Distance[p, m] / 1000; # Shipment quantities in cases var shipment{Plants, Markets} >= 0; # Total transportation costs in thousands of dollars minimize cost: sum{p in Plants, m in Markets} TransportCost[p, m] * shipment[p, m]; # Observe supply limit at plant p s.t. supply{p in Plants}: sum{m in Markets} shipment[p, m] <= Capacity[p]; # Satisfy demand at market m s.t. demand{m in Markets}: sum{p in Plants} shipment[p, m] >= Demand[m]; data; set Plants := seattle san-diego; set Markets := new-york chicago topeka; param Capacity := seattle 350 san-diego 600; param Demand := new-york 325 chicago 300 topeka 275; param Distance : new-york chicago topeka := seattle 2.5 1.7 1.8 san-diego 2.5 1.8 1.4; param Freight := 90; Solvers Here is a partial list of solvers supported by AMPL: See also sol (format) GNU MathProg (previously known as GMPL) is a subset of AMPL supported by the GNU Linear Programming Kit References External links Prof. Fourer's home page at Northwestern University 1990 software Computer algebra systems Mathematical modeling Mathematical optimization software Numerical programming languages Scripting languages Text-oriented programming languages Programming languages created in 1985 Proprietary cross-platform software