[Symphony] biobjective problems

Tue Sep 17 13:27:32 EDT 2013

I am able to get the correct answer now. Thank you,Papis

From: papis_31 at hotmail.com
Date: Mon, 16 Sep 2013 11:12:35 -0500
To: ted at lehigh.edu
CC: symphony at list.coin-or.org
Subject: Re: [Symphony] biobjective problems

I do understand now why i got all negative value. However, I got different results from your presentation online. It seems like my results are incorrect.
Best, Papis
On Sep 16, 2013, at 10:54 AM, "Ted Ralphs" <ted at Lehigh.EDU> wrote:

The bottom line is that there doesn't seem to be anything wrong with the output except that the objective value is reported as negative instead of positive because SYMPHONY converts your maximization problem into an equivalent minimization problem internally. Was there something besides that that seemed incorrect?

Cheers,

Ted

On Sun, Sep 15, 2013 at 1:48 PM, Papis Wongchaisuwat <papis_31 at hotmail.com> wrote:

I am sorry but I don't clearly understand what do you mean and how can I fix my problem.
Thank youPapis

From: ted at Lehigh.EDU
Date: Sun, 15 Sep 2013 12:45:28 -0400

Subject: Re: [Symphony] biobjective problems
To: papis_31 at hotmail.com
CC: hennebry at web.cs.ndsu.nodak.edu; symphony at list.coin-or.org

It looks correct to me (without knowing what the second objective is). SYMPHONY converts all problems to minimization internally, so the negative objective values are just because we don't check whether the problem was maximization and negate the objective values if it is. This should be easy to change. You can file a ticket and I'll try to get to it.

Ted

On Sun, Sep 15, 2013 at 12:39 PM, Papis Wongchaisuwat <papis_31 at hotmail.com> wrote:

Thank you for a reply.I tried to start from simple problem that I found in presentation online.vmax [8x1, x2]s.t. 7x1 + x2 <= 5628x1 + 9x2 <= 252

3x1 + 7x2 <=105x1, x2 >=0
In bicriteria.c, I use#include "symphony.h"
int main(int argc, char **argv)

{
   sym_environment *env = sym_open_environment();   sym_parse_command_line(env, argc, argv);   sym_load_problem(env);
   sym_set_obj2_coeff(env, 1, 1);

   sym_mc_solve(env);
   sym_close_environment(env);
   return(0);
}
my lp file :

Maximize 

obj: 8 var_1 + var_2

Subject to 

 C1: 7 var_1 + var_2 <=
56

C2: 28 var_1 + 9 var_2 <= 252

C3: 3 var_1+ 7 var_2 <= 105

Bound

var_1>=0

var_2>=0
Integer

var_1
var_2

End 

I got incorrect results. 
This is what I got

First Objective: -64.000 Second Objective: 0.000 Range: 0.468750-1.000000
First Objective: -47.000 Second Objective: -15.000 Range: 0.000000-0.468750

What did I do wrong?

Thank you,Papis

From: ted at Lehigh.EDU

Date: Sun, 15 Sep 2013 12:27:26 -0400
Subject: Re: [Symphony] biobjective problems
To: papis_31 at hotmail.com
CC: hennebry at web.cs.ndsu.nodak.edu; symphony at list.coin-or.org

sym_set_obj2_coeff(env, i, j) sets the objective function coefficient of variable "i" to value "j" in the second objective, as documented here:

http://www.coin-or.org/SYMPHONY/man-5.5/node176.html

At the moment, setting the objective coefficients one by one is the only way to specify a second objective through the API. Of course, you can also just directly set the objective function in SYMPHONY's internal representation of the instance.

I have plans to improve this and to add the ability to specify two objectives through a modeling language, such as GMPL, but I haven't gotten to it yet.

Cheers,

Ted

On Sat, Sep 14, 2013 at 10:58 PM, Papis Wongchaisuwat <papis_31 at hotmail.com> wrote:

I found  bicriteria.c file in Examples. I tried running with the data set and I got several solutions as I am supposed to get. 

However, I am not sure whether I got a correct result.These are some parts of bicriteria.c file

#include "symphony.h"
int main(int argc, char **argv){
   sym_environment *env = sym_open_environment();   sym_parse_command_line(env, argc, argv);

   sym_load_problem(env);
   sym_set_obj2_coeff(env, 1, -1);
   sym_mc_solve(env);
   sym_close_environment(env);
   return(0);

}
#endif
Does anyone know what sym_set_obj2_coeff(env, 1, -1) means?  When should I use 1 or -1?

My sample data is a minimization problem.

Thank you,Papis
> Date: Fri, 13 Sep 2013 23:29:29 -0500
> From: hennebry at web.cs.ndsu.nodak.edu

> To: papis_31 at hotmail.com
> CC: symphony at list.coin-or.org
> Subject: RE: [Symphony] biobjective problems

> 
> On Sat, 14 Sep 2013, Papis Wongchaisuwat wrote:
> 
> > I would like to run bi-objective Set cover and Set pack problems. Attached files are some examples that I want to run. MCKP and these problems are quite different. I don't know how to apply MCKP or either use any other ways to run these problems.

> 
> From reading the manual,
> I gather one can call sym_explicit_load_problem( ... )
> and follow it by calling sym_mc_solve( ... ) .
> Is there a reason that you cannot do that?
> 

> -- 

> Michael   hennebry at web.cs.ndsu.NoDak.edu
> "On Monday, I'm gonna have to tell my kindergarten class,
> whom I teach not to run with scissors,

> that my fiance ran me through with a broadsword."  --  Lily

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-- 
Dr. Ted Ralphs
Associate Professor, Lehigh University
(610) 628-1280
ted 'at' lehigh 'dot' edu

coral.ie.lehigh.edu/~ted

-- 
Dr. Ted Ralphs
Associate Professor, Lehigh University
(610) 628-1280
ted 'at' lehigh 'dot' edu

coral.ie.lehigh.edu/~ted

-- 
Dr. Ted Ralphs
Associate Professor, Lehigh University
(610) 628-1280
ted 'at' lehigh 'dot' edu
coral.ie.lehigh.edu/~ted

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