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## [Help-glpk] Beginner questions (MIP model)

 From: Denis Debarbieux Subject: [Help-glpk] Beginner questions (MIP model) Date: Tue, 24 Feb 2009 16:37:18 +0300

```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.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

```