[Help-glpk] java glpk

[David Gabriel]

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);
        }
  }