AMPL Suffixes

To represent values associated with an entity, AMPL employs various qualifiers or suffixes appended to entity names. A suffix consists of a period or “dot” (.) followed by a (usually short) identifier, so that for example the reduced cost associated with a variable Buy[j] is written Buy[j].rc, and the reduced costs of all such variables can be viewed by giving the command display Buy.rc. There are numerous built-in suffixes of this kind, available for use in any AMPL session; see our tables of built-in suffixes for details below.

AMPL cannot anticipate all of the values that a solver might associate with model components, however. The values recognized (as input) or computed (as output) depend on the design of each solver and its algorithms. To provide for the representation of these values, the concept of a suffix has been extended to permit the definition of new suffixes for the duration of an AMPL session.

The following section shows all built-in suffixes of AMPL.

Built-in Suffixes

Variables

Suffixes	Interpretation
.astatus	AMPL status (fixed, presolved, or substituted out)
.defeqn	Index in _con of “defining constraint” used to substitute variable out
.dual	Dual value on defining constraint of variable substituted out
.init	Current initial guess
.init0	Original initial guess (set by := or default or by a data statement)
.lb	Current lower bounds
.lb0	Initial lower bounds, from the var declaration
.lb1	Weaker lower bounds from AMPL’s presolve phase
.lb2	Stronger lower bounds from AMPL’s presolve phase
.lrc	Reduced costs at lower bounds
.lslack	Slacks at lower bounds (val - lb)
.rc	Reduced cost (at the nearer bound)
.relax	Ignore integrality restriction if positive
.slack	Bound slack (the lesser of lslack and uslack)
.sstatus	Solver status (basis status of variable)
.status	AMPL status if not “in”, otherwise solver status
.ub	Current upper bounds
.ub0	Initial upper bounds, from the var declaration
.ub1	Weaker upper bounds from AMPL’s presolve phase
.ub2	Stronger upper bounds from AMPL’s presolve phase
.urc	Reduced costs at upper bounds
.uslack	Slacks at upper bounds (ub - val)
.val	Current value

Constraints

To define these values unambiguously, all constraints are assumed to be put in the form lower bound <= body <= upper bound, where the the constraint body contains all terms involving variables, and the bounds are constants.

Suffixes	Interpretation
.astatus	AMPL status (dropped, presolved, or substituted out)
.body	Current value of constraint body
.defvar	Index in _var of “defined variable” substituted out by the constraint
.dinit	Current initial guess for the constraint’s dual variable
.dinit0	Original initial guess for the constraint’s dual variable
.dual	Current value of the constraint’s dual variable
.lb	Constraint lower bounds
.lbs	Constraint lower bounds sent to solver (reflecting adjustments for fixed variables)
.ldual	Current dual values associated with lower bounds
.lslack	Slacks at lower bounds (body - lb)
.slack	Constraint slack (the lesser of lslack and uslack)
.sstatus	Solver status (basis status of constraint’s slack or artificial variable)
.status	AMPL status if not “in”, otherwise solver status
.ub	Constraint upper bounds
.ubs	Constraint upper bounds sent to solver (reflecting adjustments for fixed variables)
.udual	Current dual values associated with upper bounds
.uslack	Slacks at lower & upper bounds (ub - body)

Objectives

Suffixes	Interpretation
.astatus	AMPL status
.exitcode	Exit code returned by solver after most recent solve with this objective
.message	Result message returned by solver after most recent solve with this objective
.result	Result string returned by solver after most recent solve with this objective
.val	Current value

Problems

Suffixes	Interpretation
.astatus	AMPL status
.exitcode	Exit code returned by solver after most recent solve of this problem
.message	Result message returned by solver after most recent solve of this problem
.result	Result string returned by solver after most recent solve of this problem

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