Re: [Help-glpk] glp_intopt runs forever

[Heinrich Schuchardt]

Hello Dušan,

glpsol --lp problem.lp
solves you problem easily. So the problem is not with the GLPK solver
but most probably with your code.

If you need help on the code you will have to provide more than the
short snippet.

Best regards

Heinrich Schuchardt

On 06/09/2017 04:49 PM, Dušan Plavák wrote:
> Hi guys,
> 
> I would like to ask you for a help with one lp problem. We are using
> version 4.61 with the following code:
> 
> glp_write_lp(lp, 0, "problem.lp");
> 
> glp_iocp parm;
> glp_init_iocp(&parm);
> parm.msg_lev = GLP_MSG_OFF;
> parm.presolve = GLP_ON;
> 
> glp_intopt(lp, &parm);
> 
> 
> and glp_intopt() call runs "forever". I was reading docs and found note
> there:
> /*Note that the GLPK branch-and-cut solver is not perfect, so it is
> unable to solve hard or very large scale MIP instances for a reasonable
> time.*/
> 
> The lp problem on which it freezes is following:
> 
> 
> \* Problem: amounts *\
> 
> Minimize
>  obj: + 0.03 x_6 + 0.0375 x_7 + 0.1 x_8 + 0.0333333333333333 x_9
> 
> Subject To
>  r_1: + 9.281400000008 x_5 + 2.548 x_4 + 0.17905 x_3 + 2.9625 x_2
>  + 1.0491 x_1 - ~r_1 = -80000
>  r_2: + 9.2814 x_5 + 0.744 x_4 + 0.02325 x_3 + 0.34875 x_2 + 0.0651 x_1
>  - ~r_2 = -32000
>  r_3: + 4e-12 x_5 + 0.369 x_4 + 0.10291 x_3 + 1.99875 x_2 + 0.0082 x_1
>  - ~r_3 = -12000
>  r_4: + 4e-12 x_5 + 1.435 x_4 + 0.05289 x_3 + 0.615 x_2 + 0.9758 x_1
>  - ~r_4 = -36000
>  r_5: + x_5 + 10 x_4 + x_3 + 18.75 x_2 + x_1 <= 800
>  r_6: + x_6 + 9.281400000008 x_5 + 2.548 x_4 + 0.17905 x_3 + 2.9625 x_2
>  + 1.0491 x_1 >= 400
>  r_7: - x_6 + 9.281400000008 x_5 + 2.548 x_4 + 0.17905 x_3 + 2.9625 x_2
>  + 1.0491 x_1 <= 400
>  r_8: + x_7 + 9.2814 x_5 + 0.744 x_4 + 0.02325 x_3 + 0.34875 x_2
>  + 0.0651 x_1 >= 160
>  r_9: - x_7 + 9.2814 x_5 + 0.744 x_4 + 0.02325 x_3 + 0.34875 x_2
>  + 0.0651 x_1 <= 160
>  r_10: + x_8 + 4e-12 x_5 + 0.369 x_4 + 0.10291 x_3 + 1.99875 x_2
>  + 0.0082 x_1 >= 60
>  r_11: - x_8 + 4e-12 x_5 + 0.369 x_4 + 0.10291 x_3 + 1.99875 x_2
>  + 0.0082 x_1 <= 60
>  r_12: + x_9 + 4e-12 x_5 + 1.435 x_4 + 0.05289 x_3 + 0.615 x_2
>  + 0.9758 x_1 >= 180
>  r_13: - x_9 + 4e-12 x_5 + 1.435 x_4 + 0.05289 x_3 + 0.615 x_2
>  + 0.9758 x_1 <= 180
> 
> Bounds
>  0 <= ~r_1 <= 160000
>  0 <= ~r_2 <= 64000
>  0 <= ~r_3 <= 24000
>  0 <= ~r_4 <= 72000
>  100 <= x_1 <= 400
>  8 <= x_2 <= 16
>  2 <= x_3 <= 400
>  4 <= x_4 <= 20
>  4 <= x_5 <= 30
> 
> Generals
>  x_1
>  x_2
>  x_3
>  x_4
>  x_5
> 
> End
> 
> 
> It does not seems to be large scale, and I am not sure if this is
> classified as hard problem? Also the interesting part is that on the
> older version of glpk it was solved without any problems.
> 
> Thanks for help.
> -- 
> S pozdravom Dušan Plavák
> 
> 
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