AMPLSyntax < OpsRes

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---+ The AMPL Syntax Guide

*%RED%Disclaimer%ENDCOLOR%* This is a __guide__ to the AMPL syntax only. For a comprehensive reference to the AMPL language see [[https://www.ampl.com/BOOK/index.html][AMPL: A Modeling Language for Mathematical Programming]].

   1 [[#comments][Commenting]] 
   1 [[#symbolic][Using symbolic]] 
   1 [[SetsInAMPL][Sets]] 
   1 [[VariablesInAMPL][Variables]] 
   1 [[ParametersInAMPL][Parameters]] 
   1 [[ExpressionsInAMPL][Expressions]] 
   1 [[ObjectiveFunctionsInAMPL][Objective Functions]] 
   1 [[ConstraintsInAMPL][Constraints]] 
   1 [[LogicInAMPL][Logical Statements]]
   1 [[LoopingInAMPL][Looping Statements]]
   1 [[PrintingInAMPL][Displaying and Printing]]
   1 [[MiscellaneousAMPL][Miscellaneous AMPL Commands]]

---++ <a name="comments"></a> Commenting

The =#= is used for commenting, any characters on a line after the =#= are ignored by AMPL.

---+++ Examples
[[WhiskasCatFoodProblem][The Whiskas Cat Food Problem]]

<pre># The set of all possible ingredients for the cat food set INGREDIENTS; </pre>

[[SurfboardProduction][The Surfboard Production Problem]]

<pre>
param Supply {MATERIALS}; # The supply of each raw material

param Recipe {MATERIALS, SURFBOARDS}; # The "recipe" for making surfboards
</pre>

---++ <a name="symbolic"></a> Using =symbolic=

The =symbolic= keyword is used to create parameters that represent character strings. Usually they are used to represent members of 1-dimensional sets or part of a _tuple_ for multi-dimensional sets. However, they can also be used to represent file names or to automatically build labels (for entry in a set, for example).

---+++ Example. Searching a 1-Dimensional set
<pre>
param gotcha symbolic within SET;
for {s in SET} {
   if  then
     let gotcha := s;
} # gotcha now contains the (last) element in SET that satisfies the condition
</pre>

---+++ Example. Searching a 2-Dimensional Set
<pre>
set SET1;
set SET2;

set TWO_D_SET within SET1 cross SET2;

param got_one symbolic within SET1;
param got_two symbolic within SET2;

for {(s, t)  in TWO_D_SET} {
   if  then {
     let got_one := s;
     let got_two := t;
   }
} # (got_one, got_two) now contains the (last) element in TWO_D_SET # that satisfies the condition
</pre>

To build labels for set elements you need a =symbolic= parameter and the parts of the label. You can then "glue" the parts of the label together by enclosing the label within =(= and =)= and joining the parts with =&=. The parts can be set elements, strings or numbers. Numbers are converted to strings using the [[https://www.cppreference.com/stdio/printf.html][%g format from printf]] .

---+++ Example. Dynamically Building a Set
<pre>
param name symbolic;

let SUPPLY_NODES := {};

for {s in SUPPLY_LOCATIONS} {
   let name := (s & '-Woodchips');
   let SUPPLY_NODES := SUPPLY_NODES union {name};
   let Supply[name] := MaterialSupply[s, 'Woodchips'];
   let {d in DEMAND_NODES} Cost[name, d] := TransportationCost[s, d];
   let dummyDemandCost[name] := DisposalCost['Woodchips'];
}
</pre>

-- Main.MichaelOSullivan - 27 Feb 2008
Topic revision: r9 - 2008-04-02 - MichaelOSullivan