// Compute the stable models of the program
// a :- not b.
// b :- not a.
void example1() {
// The ProgramBuilder lets you define logic programs.
// It preprocesses logic programs and converts them
// to the internal solver format.
// See program_builder.h for details.
Clasp::ProgramBuilder api;
// Among other things, SharedContext maintains a Solver object
// which hosts the data and functions for CDNL answer set solving.
// SharedContext also contains the symbol table which stores the
// mapping between atoms of the logic program and the
// propositional literals in the solver.
// See shared_context.h for details.
Clasp::SharedContext ctx;
// startProgram must be called once before we can add atoms/rules
api.startProgram(ctx);
// Populate symbol table. Each atoms must have a unique id, the name is optional.
// The symbol table then maps the ids to the propositional
// literals in the solver.
api.setAtomName(1, "a");
api.setAtomName(2, "b");
// Define the rules of the program.
api.startRule(Clasp::BASICRULE).addHead(1).addToBody(2, false).endRule();
api.startRule(Clasp::BASICRULE).addHead(2).addToBody(1, false).endRule();
// Once all rules are defined, call endProgram() to load the (simplified)
// program into the context object.
api.endProgram();
if (api.dependencyGraph() && api.dependencyGraph()->nodes() > 0) {
// The program is non tight - add unfounded set checker.
Clasp::DefaultUnfoundedCheck* ufs = new Clasp::DefaultUnfoundedCheck();
// Register with solver and graph & transfer ownership.
ufs->attachTo(*ctx.master(), api.dependencyGraph());
}
// For printing answer sets.
AspOutPrinter printer;
// Since we want to compute more than one
// answer set, we need an enumerator.
// See enumerator.h for details
ctx.addEnumerator(new Clasp::BacktrackEnumerator(0,&printer));
ctx.enumerator()->enumerate(0);
// endInit() must be called once before the search starts.
ctx.endInit();
// Aggregates some solving parameters, e.g.
// - restart-strategy
// - ...
// See solve_algorithms.h for details.
Clasp::SolveParams params;
// solve() starts the search for answer sets. It uses the
// given parameters to control the search.
Clasp::solve(ctx, params);
}
// Compute the stable models of the program
// a :- not b.
// b :- not a.
void example1(bool basicSolve) {
// LogicProgram provides the interface for
// defining logic programs.
// It also preprocesses the program and converts it
// to the internal solver format.
// See logic_program.h for details.
Clasp::Asp::LogicProgram lp;
Potassco::RuleBuilder rb;
// Among other things, SharedContext maintains a Solver object
// which hosts the data and functions for CDNL answer set solving.
// See shared_context.h for details.
Clasp::SharedContext ctx;
// startProgram must be called once before we can add atoms/rules
lp.startProgram(ctx);
// Define the rules of the program.
Potassco::Atom_t a = lp.newAtom();
Potassco::Atom_t b = lp.newAtom();
lp.addRule(rb.start().addHead(a).addGoal(Potassco::neg(b)));
lp.addRule(rb.start().addHead(b).addGoal(Potassco::neg(a)));
// Populate output table.
// The output table defines what is printed for a literal
// that is part of an answer set.
lp.addOutput("a", a);
lp.addOutput("b", b);
// It is not limited to atoms. For example, the following
// statement results in the ouput "~b" whenever b is not
// in a stable model.
lp.addOutput("~b", Potassco::neg(b));
// And we always want to have "eureka"...
lp.addOutput("eureka", Potassco::toSpan<Potassco::Lit_t>());
// Once all rules are defined, call endProgram() to load the (simplified)
// program into the context object.
lp.endProgram();
// Since we want to compute more than one
// answer set, we need an enumerator.
// See enumerator.h for details
Clasp::ModelEnumerator enumerator;
enumerator.init(ctx);
// We are done with problem setup.
// Prepare for solving.
ctx.endInit();
if (basicSolve) {
std::cout << "With Clasp::BasicSolve" << std::endl;
// BasicSolve implements a basic search for a model.
// It handles the various strategies like restarts, deletion, etc.
Clasp::BasicSolve solve(*ctx.master());
// Prepare the solver for enumeration.
enumerator.start(solve.solver());
while (solve.solve() == Clasp::value_true) {
// Make the enumerator aware of the new model and
// let it compute a new constraint and/or backtracking level.
if (enumerator.commitModel(solve.solver())) { printModel(ctx.output, enumerator.lastModel()); }
// Integrate the model into the search and thereby prepare
// the solver for the search for the next model.
enumerator.update(solve.solver());
}
std::cout << "No more models!" << std::endl;
}
else {
std::cout << "With Clasp::SequentialSolve" << std::endl;
// SequentialSolve combines a BasicSolve object,
// which implements search for a model and handles
// various strategies like restarts, deletion, etc.,
// with an enumerator to provide more complex reasoning,
// like enumeration or optimization.
Clasp::SequentialSolve solve;
solve.setEnumerator(enumerator);
// Start the solve algorithm and prepare solver for enumeration.
solve.start(ctx);
// Extract and print models one by one.
while (solve.next()) {
printModel(ctx.output, solve.model());
}
if (!solve.more()) {
std::cout << "No more models!" << std::endl;
}
}
}
