VariableInstance¶

class VariableInstance¶

A decision variable instance. Each member of this class belongs to a single Variable. Note that accessors available here are replicated at Variable level for ease of use when dealing with scalar variables.

All AMPL suffixes for an algebraic variable are available through methods with the same name in this class. See https://www.ampl.com/NEW/suffbuiltin.html for a list of the available suffixes.

All the accessors in this class throw an error if the instance has been deleted in the underlying AMPL interpreter.

VariableInstance.name()¶

Returns the name of this instance.

Returns: Name of the instance.

VariableInstance.toString()¶

Returns a string representation of this instance.

Returns: String representation of this instance.

VariableInstance.value()¶

Get the current value of this variable.

Returns: Value of the variable.

VariableInstance.fix(value=NULL)¶

Fix all instances of this variable to their current value, or to the specified value if provided.

Parameters: value (float) – The value the variable must be set to.
Returns: NULL.

VariableInstance.unfix()¶

Unfix this variable instances.

Returns: NULL.

VariableInstance.setValue()¶

Set the current value of this variable (does not fix it), equivalent to the AMPL command let

Parameters: value (float) – Value to be set.
Returns: NULL.

VariableInstance.astatus()¶

Get the variable status (fixed, presolved, or substituted out).

Returns: Variable status.
Return type: str

VariableInstance.defeqn()¶

Get the index in _con of “defining constraint” used to substitute variable out.

Returns: Index of the defining constraint.
Return type: int

VariableInstance.dual()¶

Get the dual value on defining constraint of variable substituted out.

Returns: Dual value.
Return type: float

VariableInstance.init()¶

Get the current initial guess.

Returns: The initial guess.
Return type: float

VariableInstance.init0()¶

Get the original initial guess (set by := or`default` or by a data statement)

Returns: The original initial guess.
Return type: float

VariableInstance.lb()¶

Returns the current lower bound. See Note on variables suffixes.

Returns: The current lower bound.
Return type: float

VariableInstance.ub()¶

Returns the current upper bound. See Note on variables suffixes.

Returns: The current upper bound.
Return type: float

VariableInstance.lb0()¶

Returns the initial lower bound, from the var declaration.

Returns: The intial lower bound.
Return type: float

VariableInstance.ub0()¶

Returns the initial upper bound, from the var declaration.

Returns: The intial upper bound.
Return type: float

VariableInstance.lb1()¶

Returns the weaker lower bound from AMPL’s presolve phase.

Returns: The weaker lower bound.
Return type: float

VariableInstance.ub1()¶

Returns the weaker upper bound from AMPL’s presolve phase.

Returns: The weaker upper bound.
Return type: float

VariableInstance.lb2()¶

Returns the stronger lower bound from AMPL’s presolve phase.

Returns: The stronger lower bound.
Return type: float

VariableInstance.ub2()¶

Returns the stronger upper bound from AMPL’s presolve phase.

Returns: The stronger upper bound.
Return type: float

VariableInstance.lrc()¶

Returns the reduced cost at lower bound.

Returns: The reduced cost at lower bound.
Return type: float

VariableInstance.urc()¶

Returns the reduced cost at upper bound.

Returns: The reduced cost at upper bound.
Return type: float

VariableInstance.lslack()¶

Returns the slack at lower bound (val - lb). See Note on variables suffixes.

Returns: The slack at lower bound.
Return type: float

VariableInstance.uslack()¶

Returns the slack at upper bound (ub - val). See Note on variables suffixes.

Returns: The slack at upper bound.
Return type: float

VariableInstance.rc()¶

Get the reduced cost (at the nearer bound).

Returns: The reduced cost.
Return type: float

VariableInstance.slack()¶

Returns the bound slack which is the lesser of lslack() and uslack(). See Note on variables suffixes.

Returns: The smaller slack.
Return type: float

VariableInstance.sstatus()¶

Solver status (basis status of variable).

Returns: The basis status of the variable.
Return type: str

VariableInstance.status()¶

AMPL status if not in, otherwise solver status

Returns: The status of the variable.
Return type: str

Variable

Constraint