# ConstraintInstance¶

class ampl::ConstraintInstance

This class represent an instance of a constraint.

In general, all AMPL suffixes for a constraint are available through methods with the same name in this class. See http://www.ampl.com/NEW/suffbuiltin.html for a list of the available suffixes.

Note that, since this class represents instances of both algebraic and logical constraints, some suffixes might not be available for every instance. If a wrong suffix for the specific class of constraint is accessed, an std::logic_error is thrown.

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

Public Functions

void drop()

Drop this constraint instance, corresponding to the AMPL code: drop constraintname;.

void restore()

Restore this constraint instance, corresponding to the AMPL code: restore constraintname;.

double body() const

Get the current value of the constraint’s body.

std::string astatus() const

Get the current AMPL status (dropped, presolved, or substituted out)

int defvar() const

Get the index in _var of “defined variable” substituted out by the constraint.

double dinit() const

Get the current initial guess for the constraint’s dual variable.

double dinit0() const

Get the original initial guess for the constraint’s dual variable.

double dual() const

Get the current value of the constraint’s dual variable.

Note that dual values are often reset by the underlying AMPL interpreter by the presolve functionalities triggered by some methods. A possible workaround is to set the option presolve; to false (see setBoolOption).

double lb() const

Get the current value of the constraint’s lower bound.

double ub() const

Get the current value of the constraint’s upper bound.

double lbs() const

Get the constraint lower bound sent to the solver (reflecting adjustment for fixed variables)

double ubs() const

Get the constraint upper bound sent to the solver (reflecting adjustment for fixed variables)

double ldual() const

Get the current dual value associated with the lower bound.

double udual() const

Get the current dual value associated with the upper bounds.

double lslack() const

Get the slack at lower bound body - lb

double uslack() const

Get the slack at upper bound ub - body

double slack() const

Constraint slack (the lesser of lslack and uslack)

std::string sstatus() const

Get the solver status (basis status of constraint’s slack or artificial variable)

std::string status() const

Get the AMPL status if not in, otherwise solver status.

void setDual(double dual)

Set the value of the dual variable associated to this constraint.

Equivalent to the AMPL statement:

let c := dual;

Note that dual values are often reset by the underlying AMPL interpreter by the presolve functionalities triggered by some methods. A possible workaround is to set the option presolve to false (see setBoolOption).

Parameters
• dual -

The value to be assigned to the dual variable

double val() const

Get the AMPL val suffix.

Valid only for logical constraints.