AMPLSyntax < OpsRes

---+ 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 [[href="https://www.ampl.com/BOOK/index.html][AMPL: A Modeling Language for Mathematical Programming]].

<ol>
<li><a href="#comments">Commenting</a>
<li><a href="#symbolic">Using {\tt symbolic}</a>
<li><a href="Sets in AMPL">Sets</a>
<li><a href="Variables in AMPL">Variables</a>
<li><a href="Parameters in AMPL">Parameters</a>
<li><a href="Expressions in AMPL">Expressions</a>
<li><a href="Objective Functions in AMPL">Objective Functions</a>
<li><a href="Constraints in AMPL">Constraints</a>
<li><a href="Logic in AMPL">Logical Statements</a>
<li><a href="Looping in AMPL">Looping Statements</a>
<li><a href="Printing in AMPL">Displaying and Printing</a>
<li><a href="Miscellaneous AMPL">Miscellaneous AMPL Commands</a>
</ol>

<a name="comments"><h3>Commenting</h3></a>

The {\tt #} is used for commenting, any characters after the {\tt #} are ignored by AMPL.

<h4>Examples</h4>
<a href="A Blending Problem">The Whiskas Cat Food Problem</a>
<p>\begin{verbatim}
var x1 >= 0; # Percentage chicken meat used in 100g of cat food (= g)
\end{verbatim}<p>

<a href="A Price-Production Problem">The Surfboard Production Problem</a>
<p>\begin{verbatim}
param Resin {SURFBOARDS} >= 0; # Amount of resin (in kilos) needed for a board
param TotalResin >= 0; # Total amount of resin available
\end{verbatim}<p>

<a name="symbolic"><h3>Using {\tt symbolic}</h3></a>

The {\tt 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 <i>tuple</i> 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).

<h4>Example. Searching a 1-Dimensional set</h4>
<p>\begin{verbatim}
param gotcha symbolic within SET;
for {s in SET} {
  if <condition> then
    let gotcha := s;
}
# gotcha now contains the (last) element in SET that satisfies the condition
\end{verbatim}<p>

<h4>Example. Searching a 2-Dimensional Set</h4>
<p>\begin{verbatim}
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 <condition> 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
\end{verbatim}<p>

To build labels for set elements you need a {\tt symbolic} parameter and the parts of the label. You can
then "glue" the parts of the label together by enclosing the label within {\tt (} and {\tt )} and joining
the parts with {\tt &}. The parts can be set elements, strings or numbers. Numbers are converted to strings
using the <a href="https://www.cppreference.com/stdio/printf.html">{\tt %g} format from {\tt printf}</a>.
<h4>Example. Dynamically Building a Set</h4>
<p>\begin{verbatim}
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'];
}
\end{verbatim}<p>

<a href="Sets in AMPL"><font size=+1>Sets</font></a>

<a href="Variables in AMPL"><font size=+1>Variables</font></a>

<a href="Parameters in AMPL"><font size=+1>Parameters</font></a>

<a href="Expressions in AMPL"><font size=+1>Expressions</font></a>

<a href="Objective Functions in AMPL"><font size=+1>Objective Function</font></a>

<a href="Constraints in AMPL"><font size=+1>Constraints</font></a>

<a href="Logic in AMPL"><font size=+1>Logical Statements</font></a>

<a href="Looping in AMPL"><font size=+1>Looping Statements</font></a>

<a href="Printing in AMPL"><font size=+1>Displaying and Printing</font></a>

<a href="Miscellaneous AMPL"><font size=+1>Miscellaneous AMPL Commands</font></a>

-- Main.MichaelOSullivan - 27 Feb 2008
This topic: OpsRes > WebHome > AMPLGuide > AMPLSyntax
Topic revision: r1 - 2008-02-27 - MichaelOSullivan