[Cbc] SOS issue - why infeasible?

[John Forrest]

James,

Does not look feasible to me

SOS says at most one of neg and lt can be non-zero - not that at most 
one can be positive (It would not surprise me if there were bugs with 
negative members of SOS).  That solution has both non-zero.  I presume 
you have simplified example to give to us. You could try using "pos" 
instead or if daring derive a specialized version of SOS.

John

On 06/03/18 20:04, James Howey wrote:
>
> The following is an effort to set a binary indicator (lt) if x <= 44000
>
> maximize
>
> lt
>
> SUBJECT TO
>
> x - ff - neg = 0
>
> 44000 lt + neg >= 0
>
> BOUNDS
>
> x = 1
>
> ff = 44000
>
> -44000 <= neg <= 1e15
>
> binary
>
> lt
>
> SOS
>
> set1: S1:: neg:0 lt:1
>
> END
>
> With command arguments
>
> preprocess off solve solu a
>
> The result reached is:
>
> Integer infeasible - objective value -1.00000000
>
>       0 lt 1                      -1
>
>       1 x 1                       0
>
>       2 ff 44000                       0
>
>       3 neg -43999                       0
>
> Which appears feasible to me?
>
> Any insight is appreciated.
>
> Thanks,
>
> jkh
>
>
>
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