?Expr RelOp ?Expr reifiable
defines an arithmetic constraint. The syntax for Expr and RelOp is defined by a grammar (see Syntax of Arithmetic Expressions). Note that the expressions are not restricted to being linear. Constraints over nonlinear expressions, however, will usually yield less constraint propagation than constraints over linear expressions.
Arithmetic constraints can be reified as e.g.:
| ?- X in 1..2, Y in 3..5, X#=<Y #<=> B. B = 1, X in 1..2, Y in 3..5
Linear arithmetic constraints, except equalities, maintain bounds-consistency. Their reified versions detect bounds-entailment and -disentailment.
The following constraints are among the library constraints that general arithmetic constraints compile to. They express a relation between a sum or a scalar product and a value, using a dedicated algorithm, which avoids creating any temporary variables holding intermediate values. If you are computing a sum or a scalar product, it can be much more efficient to compute lists of coefficients and variables and post a single sum or scalar product constraint than to post a sequence of elementary constraints.
sum(+Xs, +RelOp, ?Value)
where Xs is a list of domain variables, RelOp is a
relational symbol as above, and Value is an integer or a domain
variable. True if sum(Xs) RelOp Value
.
Corresponds roughly to sumlist/2
in library(lists)
.
scalar_product(+Coeffs, +Xs, +RelOp, ?Value)
scalar_product(+Coeffs, +Xs, +RelOp, ?Value, +Options)
where Coeffs is a list of length n of integers, Xs is
a list of length n of integers or domain variables, RelOp is
a relational symbol as above, and Value is a domain variable.
True if sum(Coeffs*Xs) RelOp Value
.
Options is a list that may include the following options:
among(Least,Most,Range) since release 4.3.1
If given, Least and Most should be integers and Range should be a ConstantRange (see Syntax of Indexicals). This option imposes the additional constraint on Xs that at least Least and at most Most elements belong to Range. This side-constraint invokes the algorithm of [Razakarison, Carlsson, Beldiceanu & Simonis 13].
consistency(Cons)
This can be used to control the level of consistency used by the constraint. The value is one of the following:
domain
The constraint maintains domain-consistency.
Please note: This option is only meaningful if RelOp is
#=
, and requires that any domain variables have finite bounds.
bounds
value
The constraint tries to maintain bounds-consistency (the default).
The following constraints constrain a value to be the minimum (maximum) of a given list of values.
minimum(?Value, +Xs)
where Xs is a list of domain variables, and Value is a
domain variable. True if Value is the minimum of Xs.
Corresponds to min_member/2
in library(lists)
and to
minimum/2
in MiniZinc.
maximum(?Value, +Xs)
where Xs is a list of domain variables, and Value is a
domain variable. True if Value is the maximum of Xs.
Corresponds to max_member/2
in library(lists)
and to
maximum/2
in MiniZinc.