Difference: ParametersInAMPL (3 vs. 4)

Revision 42008-03-02 - MichaelOSullivan

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META TOPICPARENT	name="AMPLSyntax"

Parameters in AMPL

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<
<

Accessing a Parameter

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>

Accessing a Parameter

Description

Parameters hold "hard" values in AMPL. The values of parameters can be defined and changed in AMPL, but a solver will not change them while looking for an optimal solution.

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... ;

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<

??? Up to here ???

Defining Multiple Parameters

Using the {\tt :} operator, multiple parameters may be defined at once. Simply state the names of the parameters and the {\tt :=} operator. Then list the set elements and values on the following rows.

\begin{verbatim} param: ... : <value1,1> <value1,2> ... <value2,1> <value2,2> ... ; \end{verbatim}

If a parameter is not defined or the default value is sufficient, use the {\tt .} operator.

\begin{verbatim}

>
>

Defining Multiple Parameters

Using the : operator, multiple parameters may be defined at once. Simply state the names of the parameters and the := operator. Then list the set elements and values on the following rows.

param:     <name1>    <name2>    ... :
<element1> <value1,1> <value1,2> ...
<element2> <value2,1> <value2,2> ...
 ;

If a parameter is not defined or the default value is sufficient, use the . operator.

model;

# The lower and upper bounds on the requirements

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FIBRE . 2.0 SALT . 0.4 ;

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\end{verbatim}

This approach also works for 2-dimensional parameters and lists, for the American Steel problem this allows us to "cut-and-paste" the list of arc properties

\begin{verbatim} From node To node Cost Minimum Maximum Youngstown Albany 500 - 1000 Youngstown Cincinnati 350 - 3000 Youngstown Kansas City 450 1000 5000 Youngstown Chicago 375 - 5000 etc \end{verbatim}

>
>

This approach also works for 2-dimensional parameters and lists, for the American Steel problem this allows us to "cut-and-paste" the list of arc properties

From node	To node	Cost	Minimum	Maximum
Youngstown	Albany	500	-	1000
Youngstown	Cincinnati	350	-	3000
Youngstown	Kansas City	450	1000	5000
Youngstown	Chicago	375	-	5000
etc

becomes

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<

\begin{verbatim}

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>

param: Cost Min Max:= Youngstown Cincinnati 350 0 3000 Youngstown 'Kansas City' 450 1000 5000 ... Chicago Gary 120 0 4000 ;

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<

\end{verbatim}

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>

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Accessing a Parameter

Parameter values are accessed by specifying the indices of the parameter you want to access within {\tt [} and {\tt ]}.

Examples

See {\tt Cost} and {\tt Contributes} below.

\begin{verbatim}

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>

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Accessing a Parameter

Parameter values are accessed by specifying the indices of the parameter you want to access within [ and ].

Examples

See Cost and Contributes below.

# Objective: minimise the cost per (100g) can

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< minimize TotalCost: sum {i in INGREDIENTS} Cost[i] * Percentage[i];

>
> minimize TotalCost: sum {i in INGREDIENTS} Cost[i] * Amount[i];

# Constraints: Meet the nutritional requirements

subject to MeetRequirement {r in REQUIREMENTS}:

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Min[r] <= sum {i in INGREDIENTS} Contributes[i, r] * Percentage[i] <= Max[r]; \end{verbatim}

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Min[r] <= sum {i in INGREDIENTS} Contributes[i, r] * Amount[i] <= Max[r];

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-- MichaelOSullivan - 02 Mar 2008

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