COIN-OR::LEMON - Graph Library

source: lemon-project-template-glpk/deps/glpk/examples/t1.cs

subpack-glpk
Last change on this file was 9:33de93886c88, checked in by Alpar Juttner <alpar@…>, 13 years ago

Import GLPK 4.47

File size: 3.4 KB
Line 
1/*Find the minimum value which satisfies the linear inequality:
2    a*x + b*y >= 1 {a,b,x,y Integers} {a,b > 0} {a,b entered on command line}
3
4  Nigel_Galloway@operamail.com
5  February 2008
6*/
7using System;
8using System.Runtime.InteropServices;
9
10unsafe class GLPK{
11  double *lp;
12  public int a;
13  public int b;
14
15  const string glpkLibrary = "libglpk.so";
16  readonly int GLP_FR = 1;
17  readonly int GLP_IV = 2;
18  readonly int GLP_DB = 4;
19  struct ConstraintMatrix{
20    public fixed int ia[3];
21    public fixed int ja[3];
22    public fixed double ar[3];
23  }
24  [DllImport(glpkLibrary, SetLastError=true)]
25  static extern double* glp_create_prob();
26  [DllImport(glpkLibrary, SetLastError=true)]
27  static extern void glp_add_rows(double* lp, int rows);
28  [DllImport(glpkLibrary, SetLastError=true)]
29  static extern void glp_add_cols(double* lp, int cols);
30  [DllImport(glpkLibrary, SetLastError=true)]
31  static extern void glp_set_col_bnds(double* lp, int col, int bound_type, double lower_bound, double upper_bound);
32  [DllImport(glpkLibrary, SetLastError=true)]
33  static extern void glp_set_col_kind(double* lp, int col, int kind);
34  [DllImport(glpkLibrary, SetLastError=true)]
35  static extern void glp_load_matrix(double* lp, int elements, int* ia, int* ja, double* ar);
36  public GLPK(int a, int b){
37    this.a = a;
38    this.b = b;
39    lp = glp_create_prob();
40    //Col 1 is x, Col 2 is y
41    glp_add_rows(lp, 1);
42    glp_add_cols(lp, 2);
43    glp_set_col_bnds(lp, 1, GLP_FR, 0.0, 0.0);
44    glp_set_col_bnds(lp, 2, GLP_FR, 0.0, 0.0);
45    glp_set_col_kind(lp, 1, GLP_IV);
46    glp_set_col_kind(lp, 2, GLP_IV);
47    //Row 1 is a*x + b*y
48    ConstraintMatrix CM = new ConstraintMatrix();
49    CM.ia[1]=1; CM.ja[1]=1; CM.ar[1]=a;
50    CM.ia[2]=1; CM.ja[2]=2; CM.ar[2]=b;
51    glp_load_matrix(lp, 2, CM.ia, CM.ja, CM.ar);
52    Console.WriteLine("Hello Nigel");
53  }
54
55  [DllImport(glpkLibrary, SetLastError=true)]
56  static extern void glp_set_row_bnds(double* lp, int row, int bound_type, double lower_bound, double upper_bound);
57  [DllImport(glpkLibrary, SetLastError=true)]
58  static extern void glp_simplex(double* lp, void* options);
59  [DllImport(glpkLibrary, SetLastError=true)]
60  static extern void glp_intopt(double* lp, void* options);
61  [DllImport(glpkLibrary, SetLastError=true)]
62  static extern double glp_mip_col_val(double* lp, int col);
63  public int betterGuess(int upper_bound){
64    //Find a new guess less than the old guess: 1 <= (a*x + b*y) <= (old guess - 1)
65    glp_set_row_bnds(lp, 1, GLP_DB, 1.0, ((double)upper_bound)-0.5);
66    glp_simplex(lp, null);
67    glp_intopt(lp, null);
68    int x = (int)glp_mip_col_val(lp, 1);
69    int y = (int)glp_mip_col_val(lp, 2);
70    int nextGuess = a*x + b*y;
71    Console.WriteLine("x = {0}, y = {1}, a*x + b*y = {2}",x,y,nextGuess);
72    return nextGuess;
73  }
74
75  [DllImport(glpkLibrary, SetLastError=true)]
76  static extern void glp_delete_prob(double* lp);
77  ~GLPK(){
78    glp_delete_prob(lp);
79    Console.WriteLine("Goodbye Nigel");
80  }
81
82}
83
84class test{
85  static bool isMinimum(int a, int b, int guess){
86    Console.WriteLine("Trying {0}",guess);
87    if (a%guess > 0) return false;
88    if (b%guess > 0) return false;
89    Console.WriteLine("Solution is {0}",guess);
90    return true;
91  }
92
93  public static void Main(string[] args){
94    Console.WriteLine("a = {0}, b = {1}",args[0], args[1]);
95    GLPK lp = new GLPK(Int32.Parse(args[0]),Int32.Parse(args[1]));
96    int guess = (lp.a > lp.b) ? lp.b : lp.a;
97    while (!isMinimum(lp.a,lp.b,guess)) guess = lp.betterGuess(guess);
98  }
99}
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