Objective

class Objective

Represents an AMPL objective. It can contain multiple objective instances, or can be scalar. Generally, numerical values are available for each specific instance, which are accessible through the function Objective.get. For scalar objective (e.g. single objective problems), direct accessors to the values are available (see functions Objective.value or Objective.message below).

For ease of use, values for the entire algebraic entity can be accessed and assigned to MATLAB vectors using the DataFrame object. To get the values use Objective.getValues.

get(key)

classmethod Objective.get(key)

Syntax

o = get(key)

Description

o = get(key) returns the ObjectiveInstance corresponding to the specified key. Note that the same effect can be achieved using MATLAB’s indexing operator (round brackets).

Input Arguments

key

The key of the objective instance to look up.

Output Arguments

o

The specified objective instance.

Example

Create an indexed objective, get a reference to an instance and explore its properties

ampl.eval('var x{i in 1..2} <= i;');
ampl.eval('maximize z{i in 1..2}: x[i];');
z = ampl.getObjective('z');
instance = z.get(1);
ampl.solve;
instance.value
instance.result
instance.message

gives:

    ans =
1

    ans =
    solved

    ans =
    CBC 2.8.2 optimal, objective -1
    0 iterations

getValues

classmethod Objective.getValues()

Syntax

df = getValues()

df = getValues(suffixes)

Description

These functions return a dataframe with all the specified suffixes of the objective, decoupled from the underlying AMPL entity. To gain access to the data, see DataFrame.

o.getValues() gets the AMPL value (equivalent to the suffix val)

o.getValues(suffixes) allows the user to specify which suffixes to get

Input Arguments

suffixes

Strings specifying which suffixes of the objective to get (see AMPL built-in suffixes).

Output Arguments

df

A dataframe containing all the specified values of the objective and its indices

Example

Create an indexed cosntraint in AMPL, then get all the values for all the suffixes for all instances in a DataFrame and display it.

ampl.eval('var x{i in 1..2} <= i;');
ampl.eval('maximize z{i in 1..2}: x[i];');
ampl.solve;

z = ampl.getObjective('z');
df = z.getValues('val', 'astatus', 'result', 'exitcode');
df

gives:

i in 1 .. 2  |  value  astatus  result  exitcode
1.0          |  1.0    in       solved  0
2.0          |  2.0    in       ?       -1

value()

classmethod Objective.value()

Syntax

v = value()

Description

v = value() Get the current value of the objective. Valid for scalar objectives only.

Output Arguments

v

The current value of the objective.

Example

Create an objective z and display its value. Then solve the problem and display the value again.

ampl.eval('var x{i in 1..2} <= i;');
ampl.eval('maximize z: sum{i in 1..2} x[i];');
z = ampl.getObjective('z')
z.value
ampl.solve
z.value

gives:

ans =
0

ans =
CBC 2.8.2 optimal, objective -3
0 iterations

ans =
3

astatus

classmethod Objective.astatus()

Syntax

v = astatus

Description

astatus Return the AMPL status for this objective. Valid for scalar objectives only.

Output Arguments

v

The AMPL status for this objective.

Example

Create an objective z and display its status. Then solve the problem and display it again.

ampl.eval('var x{i in 1..2} <= i;');
ampl.eval('maximize z: sum{i in 1..2} x[i];');
z = ampl.getObjective('z')
z.astatus
ampl.solve;
z.astatus

gives:

ans =
in

ans =
in

exitcode

classmethod Objective.exitcode()

Syntax

v = exitcode

Description

exitcode Get exit code returned by solver after most recent solve with this objective. Valid for scalar objectives only.

Output Arguments

v

The exit code returned by solver after most recent solve with this objective.

Example

Create an objective z and display its exitcode. Then solve the problem and display it again.

ampl.eval('var x{i in 1..2} <= i;');
ampl.eval('maximize z: sum{i in 1..2} x[i];');
z = ampl.getObjective('z')
z.exitcode
ampl.solve;
z.exitcode

gives:

ans =
    -1

ans =
     0

message

classmethod Objective.message()

Syntax

v = message

Description

message Get the result message returned by solver after most recent solve with this objective. Valid for scalar objectives only.

Output Arguments

v

The result message returned by solver after the most recent solve with this objective

Example

Create an objective z and display its message. Then solve the problem and display it again.

ampl.eval('var x{i in 1..2} <= i;');
ampl.eval('maximize z: sum{i in 1..2} x[i];');
z = ampl.getObjective('z')
z.message
ampl.solve;
z.message

gives:

ans =
?

ans =
CBC 2.8.2 optimal, objective -3
0 iterations

result

classmethod Objective.result()

Syntax

v = result

Description

result Get the result string returned by solver after most recent solve with this objective. Valid for scalar objectives only.

Output Arguments

v

The result string returned by solver after most recent solve with this objective.

Example

Create an objective z and display its result string. Then solve the problem and display it again.

ampl.eval('var x{i in 1..2} <= i;');
ampl.eval('maximize z: sum{i in 1..2} x[i];');
z = ampl.getObjective('z')
z.result
ampl.solve;
z.result

gives:

ans =
?

ans =
solved

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