Class: BoolExpr
A class that represents a boolean expression in the model. The expression may depend on one or more variables and therefore its value may be unknown until a solution is found.
Examples
For example, the following code creates two interval variables x
and y
and a boolean expression isBefore
that is true if x
ends before y
starts,
that is, if the end of x
is less than or equal to
the start of y
(see IntExpr.le):
let model = new CP.Model();
let x = model.intervalVar({ length: 10, name: "x" });
let y = model.intervalVar({ length: 20, name: "y" });
let isBefore = x.end().le(y.start());
let result = await CP.solve(model);
Boolean expressions can be used to create constraints using function Model.constraint. In the example above, we may require that isBefore
is
true:
model.constraint(isBefore);
Optional boolean expressions
OptalCP is using 3-value logic: a boolean expression can be true, false or absent. Typically the the expression is absent only if one or more underlying variables is absent. The value absent means that the expression doesn't have a meaning because one or more underlying variables are absent (they are not part of the solution).
Difference between constraints and boolean expressions
Boolean expressions can take arbitrary value (true, false, or absent) and can be combined into composed expressions (e.g. using and or or).
Constraints can only be true or absent (in a solution) and cannot be combined into composed expressions.
Some functions create constraints directly, e.g. Model.noOverlap.
Then, it is not necessary to to pass them to function Model.constraint.
It is also not possible to combine constraints into composed expressions
such as or(noOverlap(..), noOverlap(..))
.
Let's consider a similar example to the one above but with optional interval
variables a
and b
:
let model = new CP.Model();
let a = model.intervalVar({ length: 10, name: "a", optional: true });
let b = model.intervalVar({ length: 20, name: "b", optional: true });
let isBefore = a.end().le(b.start());
model.constraint(isBefore);
let result = await CP.solve(model);
The function Model.constraint requires that the constraint cannot be false in a solution. It could be absent though. Therefore, in our example, there are four kinds of solutions:
- Both
a
andb
are present anda
ends beforeb
starts. - Only
a
is present andb
is absent. - Only
b
is present anda
is absent. - Both
a
andb
are absent.
In the case 1 the expression isBefore
is true. In all the other cases
isBefore
is absent as at least one of the variables a
and b
is
absent, and then isBefore
doesn't have a meaning.
Boolean expressions as integer expressions
Class BoolExpr
derives from IntExpr. Therefore boolean expressions can be used
as integer expressions. In this case true is equal to 1, false is
equal to 0, and absent remains absent.
Extends
Methods
abs()
abs():
IntExpr
Creates an integer expression which is absolute value of the expression.
Returns
Inherited from
Remarks
If the expression has value absent then the resulting expression has also value absent.
Same as Model.abs.
and()
Returns logical AND of the expression and arg
.
Parameters
Parameter | Type |
---|---|
arg | boolean | BoolExpr |
Returns
Remarks
If the expression or arg
has value absent then the resulting expression has also value absent.
Same as Model.and.
div()
Returns integer division of the expression arg
. The division rounds towards zero.
Parameters
Parameter | Type |
---|---|
arg | number | IntExpr |
Returns
Inherited from
Remarks
If the expression or arg
has value absent then the resulting expression has also value absent.
Same as Model.div.
eq()
Creates Boolean expression this
= arg
.
Parameters
Parameter | Type |
---|---|
arg | number | IntExpr |
Returns
Inherited from
Remarks
If the expression or arg
has value absent then the resulting expression has also value absent.
Use function Model.constraint to create a constraint from this expression.
Same as Model.eq.
ge()
Creates Boolean expression this
≥ arg
.
Parameters
Parameter | Type |
---|---|
arg | number | IntExpr |
Returns
Inherited from
Remarks
If the expression or arg
has value absent then the resulting expression has also value absent.
Use function Model.constraint to create a constraint from this expression.
Same as Model.ge.
getName()
getName():
undefined
|string
Returns the name assigned to the node.
Returns
undefined
| string
Inherited from
gt()
Creates Boolean expression this
> arg
.
Parameters
Parameter | Type |
---|---|
arg | number | IntExpr |
Returns
Inherited from
Remarks
If the expression or arg
has value absent then the resulting expression has also value absent.
Use function Model.constraint to create a constraint from this expression.
Same as Model.gt.
guard()
guard(
absentValue
:number
):IntExpr
Creates an expression that replaces value absent by a constant.
Parameters
Parameter | Type | Default value |
---|---|---|
absentValue | number | 0 |
Returns
Inherited from
Remarks
The resulting expression is:
- equal to the expression if the expression is present
- and equal to
absentValue
otherwise (i.e. when the expression is absent).
The default value of absentValue
is 0.
The resulting expression is never absent.
Same as Model.guard.
identity()
identity(
arg
:number
|IntExpr
):void
Constrains the expression to be identical to the argument, including their presence status.
Parameters
Parameter | Type |
---|---|
arg | number | IntExpr |
Returns
void
Inherited from
Remarks
Identity is different than equality. For example, if x
is absent, then x.eq(0)
is absent, but x.identity(0)
is false.
Same as Model.identity.
implies()
Returns implication between the expression and arg
.
Parameters
Parameter | Type |
---|---|
arg | boolean | BoolExpr |
Returns
Remarks
If the expression or arg
has value absent then the resulting expression has also value absent.
Same as Model.implies.
inRange()
inRange(
lb
:number
,ub
:number
):BoolExpr
Creates Boolean expression lb
≤ this
≤ ub
.
Parameters
Parameter | Type |
---|---|
lb | number |
ub | number |
Returns
Inherited from
Remarks
If the expression has value absent then the resulting expression has also value absent.
Use function Model.constraint to create a constraint from this expression.
Same as Model.inRange.
le()
Creates Boolean expression this
≤ arg
.
Parameters
Parameter | Type |
---|---|
arg | number | IntExpr |
Returns
Inherited from
Remarks
If the expression or arg
has value absent then the resulting expression has also value absent.
Use function Model.constraint to create a constraint from this expression.
Same as Model.le.
lt()
Creates Boolean expression this
< arg
.
Parameters
Parameter | Type |
---|---|
arg | number | IntExpr |