Hi,
It is the first I am using GLPK, and I should integrate it to my Java
project.
I succeed to install it in linux environment and I start reading some code
source examples (only 2 examples availbale in the official documentation).
I have some questions about setting constraints (columns).
In fact, I want to know why we should use integer array and double array ?
What is their lenght (is it constraint number) ?
Shall I use an array for each constraint (column) ?
Which values should be used to set the table ?
What is the importance of this statment ? :
GLPK.glp_set_mat_row(lp, 1, 2, ind, val);
What are the 2nd and the 3rd parameters of this function ?
I am looking for your help !
Thanks in advance.
Regards,
///The example I am speaking about : It is available at the official
documentation of java-glpk
// Minimize z = (x1-x2) /2 + (1-(x1-x2)) = -.5 * x1 + .5 * x2 + 1
// subject to
// 0.0<= x1 - x2 <= 0.2
// where,
// 0.0 <= x1 <= 0.5
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, 2);
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);
// Create constraints
GLPK.glp_add_rows(lp, 1);
GLPK.glp_set_row_name(lp, 1, "c1");
GLPK.glp_set_row_bnds(lp, 1, GLPKConstants.GLP_DB, 0, 0.2);
ind = GLPK.new_intArray(3);
GLPK.intArray_setitem(ind, 1, 1);
GLPK.intArray_setitem(ind, 2, 2);
val = GLPK.new_doubleArray(3);
GLPK.doubleArray_setitem(val, 1, 1.);
GLPK.doubleArray_setitem(val, 2, -1.);
GLPK.glp_set_mat_row(lp, 1, 2, ind, 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);
// 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();
}
}
/**
* 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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