[Help-glpk] Beginner questions (MIP model)

[Denis Debarbieux]

Dear GLPK users,

I am a new GLPK user and I develop under Java. I would like to write a 
simple MIP model but I do not get the good answer. Could you help me please?

I send you: my model, my code and the print problem.

/**
 *
 * integer variable: 0 <= x <= 10;
 * constraint:  x >= 7.2;
 * minimize x;
 *
 * Expected solution: x = 8
 * Return value:      x = 7.2
 */
    public static void main (String[] args) {
       
        //     initialization of solver
        GlpkSolver solver = new GlpkSolver();
        solver.addCols(1);
        solver.addRows(1);
        solver.setClss(GlpkSolver.LPX_MIP);
       
        // integer variable: 0 <= x <= 10;
        int x = 1;
        solver.setColName(x, "x");
        solver.setColBnds(1, GlpkSolver.LPX_DB, 0, 10);
        solver.setColKind(x, GlpkSolver.LPX_IV);
       
        // constraint: x >= 7.2;
        solver.setMatCol(x, 1, new int[]{NOT_USED, 1}, new 
double[]{NOT_USED, 1});
        solver.setRowBnds(x, GlpkSolver.LPX_LO, 7.2, NOT_USED);
       
        // minimize x;
        solver.setObjCoef(x, 1);
       
        // print the problem
        solver.printProb("pb.txt");
       
        // solve
        solver.simplex(); // if I remove this line, I get an error: 
optimal solution of LP relaxation required
        solver.integer();
       
        // print the solution
        System.out.println("x= "+solver.getColPrim(x));     
    }

Here is the pb.txt file:

Problem:    (unnamed)
Class:      MIP
Rows:       1
Columns:    1 (1 integer, 0 binary)
Non-zeros:  1

*** OBJECTIVE FUNCTION ***

Minimize: (unnamed)
                     1 x

*** ROWS (CONSTRAINTS) ***

Row 1: R.1 >= 7.2
                     1 x

*** COLUMNS (VARIABLES) ***

Col 1: x integer >= 0 <= 10
                     1 (objective)
                     1 R.1

End of output


Regards,

Denis