[AMPL 2828] "all variables eliminated, but lower bound = 1 > 0"

[waa15]

Hi,

I wonder if anyone can help me with the following problem :
I get a message like:

---
presolve, constraint d_39[2,5]:
        all variables eliminated, but lower bound = 1 > 0
presolve, constraint d_39[2,3]:
        all variables eliminated, but lower bound = 1 > 0
presolve, constraint d_17[2,5]:
        all variables eliminated, but lower bound = 1 > 0
presolve, constraint d_17[1,3]:
        all variables eliminated, but lower bound = 1 > 0
presolve, constraint d_39[3,1]:
        all variables eliminated, but lower bound = 1 > 0
3 presolve messages suppressed.

Presolve eliminates 20826 constraints and 3467 variables.
Adjusted problem:
11188 variables, all linear
11508 constraints, all linear; 26292 nonzeros
1 linear objective; 915 nonzeros.
---

when I try to run my model in AMPL.
The variables in question, d_XD_p_d_k, are binary and the constraint
is something like:

---
# eq d_39
subject to d_39 { p in d_P, d in d_D } :
        sum{ k in d_K } d_XD_p_d_k[p,d,k] >= d_XDMIN_p_d[p,d]
;
---

where d_XDMIN_p_d are either 0 or 1 as well.

I'll appreciate any suggestions and/or tips.

Regards

WAA



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[Paul A. Rubin]

Your model is infeasible.  One way to isolate the problem is to
fabricate a solution that should be feasible (does not need to be
anywhere near optimal), plug it into the model, and look for
violations.  The violation will not necessarily be in d_39 --
something somewhere else may for instance force a binary variable that
is zero in your solution to be 1.

/Paul

On Sep 16, 6:26 pm, waa15 <adebayo.al...@...> wrote:

> Hi,
>
> I wonder if anyone can help me with the following problem :
> I get a message like:
>
> ---
> presolve, constraint d_39[2,5]:
>         all variables eliminated, but lower bound = 1 > 0
> presolve, constraint d_39[2,3]:
>         all variables eliminated, but lower bound = 1 > 0
> presolve, constraint d_17[2,5]:
>         all variables eliminated, but lower bound = 1 > 0
> presolve, constraint d_17[1,3]:
>         all variables eliminated, but lower bound = 1 > 0
> presolve, constraint d_39[3,1]:
>         all variables eliminated, but lower bound = 1 > 0
> 3 presolve messages suppressed.
>
> Presolve eliminates 20826 constraints and 3467 variables.
> Adjusted problem:
> 11188 variables, all linear
> 11508 constraints, all linear; 26292 nonzeros
> 1 linear objective; 915 nonzeros.
> ---
>
> when I try to run my model in AMPL.
> The variables in question, d_XD_p_d_k, are binary and the constraint
> is something like:
>
> ---
> # eq d_39
> subject to d_39 { p in d_P, d in d_D } :
>         sum{ k in d_K } d_XD_p_d_k[p,d,k] >= d_XDMIN_p_d[p,d]
> ;
> ---
>
> where d_XDMIN_p_d are either 0 or 1 as well.
>
> I'll appreciate any suggestions and/or tips.
>
> Regards
>
> WAA

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