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import org.gnu.glpk.GLPK;
import org.gnu.glpk.GLPKConstants;
import org.gnu.glpk.GlpkException;
import org.gnu.glpk.SWIGTYPE_p_double;
import org.gnu.glpk.SWIGTYPE_p_int;
import org.gnu.glpk.glp_prob;
import org.gnu.glpk.glp_smcp;
public class Lp {
// Minimize z = -.5 * x1 + .5 * x2 - x3 + 1
//
// subject to
// 0.0 <= x1 - .5 * x2 <= 0.2
// -x2 + x3 <= 0.4
// where,
// 0.0 <= x1 <= 0.5
// 0.0 <= x2 <= 0.5
// 0.0 <= x3 <= 0.5
public static void main(String[] arg) {
glp_prob lp;
glp_smcp parm;
SWIGTYPE_p_int ind;
SWIGTYPE_p_double val;
int ret;
try {
// Create problem
lp = GLPK.glp_create_prob();
System.out.println("Problem created");
GLPK.glp_set_prob_name(lp, "myProblem");
// Define columns
GLPK.glp_add_cols(lp, 3);
GLPK.glp_set_col_name(lp, 1, "x1");
GLPK.glp_set_col_kind(lp, 1, GLPKConstants.GLP_CV);
GLPK.glp_set_col_bnds(lp, 1, GLPKConstants.GLP_DB, 0, .5);
GLPK.glp_set_col_name(lp, 2, "x2");
GLPK.glp_set_col_kind(lp, 2, GLPKConstants.GLP_CV);
GLPK.glp_set_col_bnds(lp, 2, GLPKConstants.GLP_DB, 0, .5);
GLPK.glp_set_col_name(lp, 3, "x3");
GLPK.glp_set_col_kind(lp, 3, GLPKConstants.GLP_CV);
GLPK.glp_set_col_bnds(lp, 3, GLPKConstants.GLP_DB, 0, .5);
// Create constraints
// Allocate memory
ind = GLPK.new_intArray(3);
val = GLPK.new_doubleArray(3);
// Create rows
GLPK.glp_add_rows(lp, 2);
// Set row details
GLPK.glp_set_row_name(lp, 1, "c1");
GLPK.glp_set_row_bnds(lp, 1, GLPKConstants.GLP_DB, 0, 0.2);
GLPK.intArray_setitem(ind, 1, 1);
GLPK.intArray_setitem(ind, 2, 2);
GLPK.doubleArray_setitem(val, 1, 1.);
GLPK.doubleArray_setitem(val, 2, -.5);
GLPK.glp_set_mat_row(lp, 1, 2, ind, val);
GLPK.glp_set_row_name(lp, 2, "c2");
GLPK.glp_set_row_bnds(lp, 2, GLPKConstants.GLP_UP, 0, 0.4);
GLPK.intArray_setitem(ind, 1, 2);
GLPK.intArray_setitem(ind, 2, 3);
GLPK.doubleArray_setitem(val, 1, -1.);
GLPK.doubleArray_setitem(val, 2, 1.);
GLPK.glp_set_mat_row(lp, 2, 2, ind, val);
// Free memory
GLPK.delete_intArray(ind);
GLPK.delete_doubleArray(val);
// Define objective
GLPK.glp_set_obj_name(lp, "z");
GLPK.glp_set_obj_dir(lp, GLPKConstants.GLP_MIN);
GLPK.glp_set_obj_coef(lp, 0, 1.);
GLPK.glp_set_obj_coef(lp, 1, -.5);
GLPK.glp_set_obj_coef(lp, 2, .5);
GLPK.glp_set_obj_coef(lp, 3, -1);
// Write model to file
// GLPK.glp_write_lp(lp, null, "lp.lp");
// Solve model
parm = new glp_smcp();
GLPK.glp_init_smcp(parm);
ret = GLPK.glp_simplex(lp, parm);
// Retrieve solution
if (ret == 0) {
write_lp_solution(lp);
} else {
System.out.println("The problem could not be solved");
}
// Free memory
GLPK.glp_delete_prob(lp);
} catch (GlpkException ex) {
ex.printStackTrace();
ret = 1;
}
System.exit(ret);
}
/**
* write simplex solution
* @param lp problem
*/
static void write_lp_solution(glp_prob lp) {
int i;
int n;
String name;
double val;
name = GLPK.glp_get_obj_name(lp);
val = GLPK.glp_get_obj_val(lp);
System.out.print(name);
System.out.print(" = ");
System.out.println(val);
n = GLPK.glp_get_num_cols(lp);
for (i = 1; i <= n; i++) {
name = GLPK.glp_get_col_name(lp, i);
val = GLPK.glp_get_col_prim(lp, i);
System.out.print(name);
System.out.print(" = ");
System.out.println(val);
}
}
}
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