Re: [Help-glpk] use GLPK to solve LP without printing anything on terminal

[Nigel Galloway]

Have you considered looking at t1.cs from glpk's example directory and glpk's API documentation?

 

Let us look now at t1.cs.

 

First the example was written for Linux so we change the line

 

    const string glpkLibrary = "libglpk.so";

to

    const string glpkLibrary = "glpk.dll";    //***

 

and run it as is "t1.exe 98 1001" produces:

a = 98, b = 1001
Hello Nigel
Trying 98
GLPK Simplex Optimizer, v4.55
1 row, 2 columns, 2 non-zeros
      0: obj =  0.000000000e+000  infeas = 1.000e+000 (0)
*     1: obj =  0.000000000e+000  infeas = 0.000e+000 (0)
OPTIMAL LP SOLUTION FOUND
GLPK Integer Optimizer, v4.55
1 row, 2 columns, 2 non-zeros
2 integer variables, none of which are binary
Integer optimization begins...
+     1: mip =     not found yet >=              -inf        (1; 0)
Solution found by heuristic: 0
+     2: mip =  0.000000000e+000 >=     tree is empty   0.0% (0; 5)
INTEGER OPTIMAL SOLUTION FOUND
x = -10, y = 1, a*x + b*y = 21
Trying 21
GLPK Simplex Optimizer, v4.55
1 row, 2 columns, 2 non-zeros
*     2: obj =  0.000000000e+000  infeas = 0.000e+000 (0)
OPTIMAL LP SOLUTION FOUND
GLPK Integer Optimizer, v4.55
1 row, 2 columns, 2 non-zeros
2 integer variables, none of which are binary
Integer optimization begins...
+     2: mip =     not found yet >=              -inf        (1; 0)
Solution found by heuristic: 0
+     2: mip =  0.000000000e+000 >=     tree is empty   0.0% (0; 3)
INTEGER OPTIMAL SOLUTION FOUND
x = 41, y = -4, a*x + b*y = 14
Trying 14
GLPK Simplex Optimizer, v4.55
1 row, 2 columns, 2 non-zeros
*     2: obj =  0.000000000e+000  infeas = 0.000e+000 (0)
OPTIMAL LP SOLUTION FOUND
GLPK Integer Optimizer, v4.55
1 row, 2 columns, 2 non-zeros
2 integer variables, none of which are binary
Integer optimization begins...
+     2: mip =     not found yet >=              -inf        (1; 0)
Solution found by heuristic: 0
+     3: mip =  0.000000000e+000 >=     tree is empty   0.0% (0; 5)
INTEGER OPTIMAL SOLUTION FOUND
x = -51, y = 5, a*x + b*y = 7
Trying 7
Solution is 7
Goodbye Nigel

All this output from glpk shows its working but is distracting so:

 

1. define GLP_OFF. In C# 5 these constants would better in an enum say GPL so we could then use GLP.OFF but this is the example written in 2008 that we have for now.

 

    readonly int GLP_OFF = 0;                 //***

 

2. add the link into glpk.dll for glp_term_out:

 

    [DllImport(glpkLibrary, SetLastError = true)]  //***

    static extern int glp_term_out(int flag);          //***

 

3. use it to turn glpk's terminal output off:

 

        glp_term_out(GLP_OFF);                //***

 

compiling and running this version "t1.exe 98 1001" produces:

 

a = 98, b = 1001

Hello Nigel

Trying 98

x = -10, y = 1, a*x + b*y = 21

Trying 21

x = 41, y = -4, a*x + b*y = 14

Trying 14

x = -51, y = 5, a*x + b*y = 7

Trying 7

Solution is 7

Goodbye Nigel

 

which I hope is close to what you want.

 

I have attached the modified t1.cs with the changes marked by //***

--

Nigel Galloway

address@hidden

 

 

 

On Sat, Apr 11, 2015, at 07:04 AM, usa usa wrote:

Also,

 

How to indicate algorithms in GLPK to solve LP or IP from API ?

 

GLPK has simplex, primal-dual and branch-bound algorithms, are there others?

 

thanks

 

On Sat, Apr 11, 2015 at 8:39 AM, Nigel Galloway <address@hidden> wrote:

If you are using the API then the output is controlled with GLP_ON and GLP_OFF. If you are using mathprog & glpsol then -y filename will send the output to a file rather than your terminal. If using Linux and you absolutely don't want the output then -y /dev/nul should do you.

 

--

Nigel Galloway

address@hidden

 

 

 

On Fri, Apr 10, 2015, at 08:24 PM, usa usa wrote:

Hi,

 

I am using GLPK to solve some linear programming models.

 

The model size is 200k variables and has one constraint.

 

It took GLPK 13 minutes to load data and build the LP model.

 

But, it took GLPK 17 minutes to solve it.

 

Is it normal ? Why building a model took so long time ?

 

Also, when GLPK is solving the model, it print out the detailed process of solving model on the command line terminal.

 

How to make GLPK to solve the model silently without printing anything on terminal ?

 

Thanks

 

 

 

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t1.cs
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