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Description
Interface Summary  

SolAccessor<V extends Var<Info>,Info>  SolAccessor provides access to the values of the
variables from a system of constraints. 
SolReader<V extends Var<Info>,Info>  SolReader provides readonly access to the (possibly
partial) solution of a system of constraints. 
Class Summary  

Constraint<V extends Var<Info>,Info>  Constraint models a constraint between several
variables. 
ConstraintSystem<V extends Var<Info>,Info>  ConstraintSystem is an efficient solver for a system
of constraints. 
CtConstraint<V extends Var<Info>,Info>  CtConstraint models a constraint of the form
"constant ct is less than the value of the
variable vd ". 
LtConstraint<V extends Var<Info>,Info>  LtConstraint models a "less than"
constraint: the value of variable vs is smaller than
the value of variable vd , according to the order
relation from the corresponding lattice. 
Var<Info>  Var models a variable from a system of constraints. 
Generic solver for inequality constraints over lattices.
This package provides a generic way of modeling and solving systems of inequality constraints over lattices. This package deals with constraints of the form
f(vi_1,vi_2,...,vi_m) <= <vo_1,vo_2,...,vo_n>
where the ordering relation <=
is specific to the
relevant lattices. The function f
is not defined
in a specialized declarative language: instead, it is defined as a
Java method that reads the values of the input variables vi_1,
..., vi_m
, computes some values, and finally joins the computed
values to the output variables vo_1, ..., vo_m
; the
constraints access the values of the variables through a welldefined
interface (SolAccessor
). The
programmer can define new constraints by subclassing the Constraint
class.
A system of constraints may involve variables that take values in different lattices: e.g., the values of some variables are sets of atoms, while the values of some other variables are binary relations between atoms. As such, this package generalizes usual set constraint solvers. Of course, specialized set solvers may be much faster and you are encouraged to take a look over them too.
The essential classes from this package are
Var
 variables; also, each variable
carries with it the operations of the lattice it takes values in;
Constraint
 general form of
a constraint; each constraint should subclass this class;
ConstraintSystem
 an efficient constraint solver.
Classes from this package are parameterized over the type of variables
(always a subtype of Var
) and the common supertype of the
classes representing the value lattices (in the extreme case, if there
is no better supertype, this type parameter can be Object
).
If we have several value lattices, certain type errors cannot be
detected statically: e.g., a constraint that states that a binary
relation is included in a set of atoms will trigger a dynamic
exception. The program should be careful about this aspect when
writting constraints.
To use this package, the programmer must follow the following steps
Var
for each
kind of variables: e.g., one subclass for the variables that have set
values and one subclass for the variables that have relation values.
The essential point here is to define the latticerelated operations
copy
and join
. In addition, it is usually a good
idea to add some debug information; e.g., override the default Var.toString
method.
Constraint
for each kind of constraints.
This package already contains two very basic kinds of constraints
(CtConstraint
and LtConstraint
), but you usually need to
define your own constraints too. Here is a sample constraint
implementation: simplified SetConstraints.IntersectConstraint.
ConstraintSystem
to solve them.
[ ConstraintSystem
works in two steps: first, it computes some data structures that allow
the efficient computation of a fixedpoint solution; next, we can
solve it several times, at different moments in time: if some of the
constraints use external values that change, the solutions may be
different. So, ConstraintSystem
is an optimized constraint system schema that
can be efficiently solved several times. ]
jpaul.Constraints.SetConstraints


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