# The AMPL Syntax Guide

Disclaimer This is a guide to the AMPL syntax only. For a comprehensive reference to the AMPL language see AMPL: A Modeling Language for Mathematical Programming.

## Commenting

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

### Examples

The Whiskas Cat Food Problem

`# The set of all possible ingredients for the cat food set INGREDIENTS; `

```param Supply {MATERIALS}; # The supply of each raw material

param Recipe {MATERIALS, SURFBOARDS}; # The "recipe" for making surfboards
```

## 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

```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
```

### Example. Searching a 2-Dimensional Set

```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
```

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 %g format from printf .

### Example. Dynamically Building a Set

```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'];
}
```

-- MichaelOSullivan - 27 Feb 2008

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Topic revision: r8 - 2008-03-18 - TWikiAdminUser

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