Re: [Help-glpk] Save solution in GLPK

[Ali Baharev]

Hello,

At the second call of lpx_simplex your problem is primal infeasible so
phase I of the primal simplex is invoked, that is why you see 0 at the
objective value. At iteration 44, it reaches feasibilty and switches
to phase II.

It seems to me that you would like to re-optimize your problem. Is
your problem dual feasible at the second call of lpx_simplex? If so,
you should use dual simplex. Just call lpx_set_int_parm(lp,
LPX_K_DUAL, 1); before lpx_simplex.

Good luck,

Ali

On 6/5/07, Cedric[FR] <address@hidden> wrote:
> Hi,
>
> In fact, I implement a column generation.
>
> But, when I started again the GLPK simplex, the counter is incrementing.
>
> But I want to initialize my solver by the precedent solution obtained
>
> For example, I obtain:
>
>       0:   objval =   0.000000000e+00   infeas =   1.000000000e+00 (0)
>      15:   objval =   3.497400000e+04   infeas =   0.000000000e+00 (0)
> *    15:   objval =   3.497400000e+04   infeas =   0.000000000e+00 (0)
> *    29:   objval =   2.652371454e+02   infeas =   0.000000000e+00 (0)
> OPTIMAL SOLUTION FOUND
>      29:   objval =   0.000000000e+00   infeas =   1.000000000e+00 (0)
>      44:   objval =   3.497400000e+04   infeas =   0.000000000e+00 (0)
> *    44:   objval =   3.497400000e+04   infeas =   0.000000000e+00 (0)
> *    58:   objval =   6.586143114e+01   infeas =   0.000000000e+00 (0)
> OPTIMAL SOLUTION FOUND
>
> At the second simplex, GLPK starts with an objval=0 instead of the precedent
> solution.
>
> Why?
>
> did I use the routine lpx_warm_up?
>
> thanks
>
>
> Andrew Makhorin wrote:
> >
> >> How can I save the precedent solution in GLPK?
> >
> >> In fact, I add a new column at problem. And, I want to initialize my
> >> solver by the precedent solution obtained.
> >
> > Do nothing. The current basis (i.e. the set of row and column statuses)
> > is always kept in the problem object.
> >
> > However, if you then need to re-optimize your instance, make sure that
> > before a call to lpx_simplex the lp presolver is disabled.
> >
> >
> >
> > _______________________________________________
> > Help-glpk mailing list
> > address@hidden
> > http://lists.gnu.org/mailman/listinfo/help-glpk
> >
> >
>
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>
>
>
>
>
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