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package samples.integer;
import samples.AbstractProblem;
import solver.ResolutionPolicy;
import solver.Solver;
import solver.constraints.IntConstraintFactory;
import solver.constraints.LogicalConstraintFactory;
import solver.variables.BoolVar;
import solver.variables.IntVar;
import solver.variables.VariableFactory;
/**
* A curriculum is a set of courses with prerequisites.
* <p/>
* Each course must be assigned within a set number of periods.
* <p/>
* A course cannot be scheduled before its prerequisites.
* <p/>
* Each course confers a number of academic credits (it's "load").
* <p/>
* Students have lower and upper bounds on the number of credits
* they can study for in a given period.
* <p/>
* Students have lower and upper bounds on the number of courses
* they can study for in a given period.
* <p/>
* The goal is to assign a period to every course satisfying these
* criteria, minimising the load for all periods.
* <br/>
*
* @author Charles Prud'homme
* @since 20/07/12
*/
public class BACP extends AbstractProblem {
int n_courses = 50;
int n_periods = 10;
int load_per_period_lb = 2;
int load_per_period_ub = 100;
int courses_per_period_lb = 2;
int courses_per_period_ub = 10;
int[] course_load =
{6, 3, 5, 3, 7, 8, 1, 9,
4, 9, 8, 8, 4, 5,
6, 3, 2, 1, 3, 1,
1, 2, 6, 7, 6, 10,
10, 1, 7, 3, 4, 2, 7,
9, 7, 4, 6, 7, 2, 2,
5, 9, 9, 10, 4, 6, 4,
5, 6, 6};
IntVar[] course_period;
BoolVar[][] x;
IntVar[] load;
IntVar objective;
@Override
public void createSolver() {
solver = new Solver("BACP");
}
@Override
public void buildModel() {
// period is assigned to
course_period = VariableFactory.enumeratedArray("c_p", n_courses, 0, n_periods, solver);
// whether period i has a course j assigned
x = VariableFactory.boolMatrix("X", n_periods, n_courses, solver);
// total load for each period
load = VariableFactory.enumeratedArray("load", n_periods, 0, load_per_period_ub - load_per_period_lb + 1, solver);
// opt. target
objective = VariableFactory.bounded("objective", load_per_period_lb, load_per_period_ub, solver);
// sum variable
IntVar sum = VariableFactory.bounded("courses_per_period", courses_per_period_lb, courses_per_period_ub, solver);
// constraints
for (int i = 0; i < n_periods; i++) {
//forall(c in courses) (x[p,c] = bool2int(course_period[c] = p)) /\
for (int j = 0; j < n_courses; j++) {
solver.post(
LogicalConstraintFactory.ifThenElse(x[i][j],
IntConstraintFactory.arithm(course_period[j], "=", i),
IntConstraintFactory.arithm(course_period[j], "!=", i))
);
}
// sum(i in courses) (x[p, i])>=courses_per_period_lb /\
// sum(i in courses) (x[p, i])<=courses_per_period_ub /\
solver.post(IntConstraintFactory.sum(x[i], sum));
// load[p] = sum(c in courses) (x[p, c]*course_load[c])/\
solver.post(IntConstraintFactory.scalar(x[i], course_load, load[i]));
// load[p] >= load_per_period_lb /\
solver.post(IntConstraintFactory.arithm(load[i], ">=", load_per_period_lb));
// load[p] <= objective
solver.post(IntConstraintFactory.arithm(load[i], "<=", objective));
}
prerequisite(3, 1);
prerequisite(4, 1);
prerequisite(5, 1);
prerequisite(6, 1);
prerequisite(7, 1);
prerequisite(6, 2);
prerequisite(8, 2);
prerequisite(11, 3);
prerequisite(11, 4);
prerequisite(16, 4);
prerequisite(16, 5);
prerequisite(11, 6);
prerequisite(14, 6);
prerequisite(16, 8);
prerequisite(13, 9);
prerequisite(14, 9);
prerequisite(17, 11);
prerequisite(19, 11);
prerequisite(17, 12);
prerequisite(19, 12);
prerequisite(18, 13);
prerequisite(17, 14);
prerequisite(18, 14);
prerequisite(23, 17);
prerequisite(21, 19);
prerequisite(26, 21);
prerequisite(27, 21);
prerequisite(30, 22);
prerequisite(24, 23);
prerequisite(25, 23);
prerequisite(27, 23);
prerequisite(33, 25);
prerequisite(34, 27);
prerequisite(35, 27);
prerequisite(35, 28);
prerequisite(33, 29);
prerequisite(34, 29);
prerequisite(35, 30);
prerequisite(36, 31);
prerequisite(38, 31);
prerequisite(39, 31);
prerequisite(40, 31);
prerequisite(43, 31);
prerequisite(40, 32);
prerequisite(37, 33);
prerequisite(38, 33);
prerequisite(40, 33);
prerequisite(38, 34);
prerequisite(41, 34);
prerequisite(41, 35);
prerequisite(42, 35);
prerequisite(44, 36);
prerequisite(45, 36);
prerequisite(45, 37);
prerequisite(44, 40);
prerequisite(45, 40);
prerequisite(47, 40);
prerequisite(44, 41);
prerequisite(45, 41);
prerequisite(46, 41);
prerequisite(46, 42);
prerequisite(47, 42);
prerequisite(48, 47);
prerequisite(44, 43);
prerequisite(45, 43);
prerequisite(49, 46);
prerequisite(50, 47);
}
private void prerequisite(int a, int b) {
solver.post(IntConstraintFactory.arithm(course_period[b - 1], "<", course_period[a - 1]));
}
@Override
public void configureSearch() {
}
@Override
public void solve() {
solver.findOptimalSolution(ResolutionPolicy.MINIMIZE, objective);
}
@Override
public void prettyOut() {
}
public static void main(String[] args) {
new BACP().execute(args);
}
}