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## Re: [Help-glpk] Network problems: remap columns to arcs

**From**: |
Andrew Makhorin |

**Subject**: |
Re: [Help-glpk] Network problems: remap columns to arcs |

**Date**: |
Wed, 5 Aug 2009 02:06:40 +0400 |

>* GLPK 4.39 provides the possibility to model networks and solve maximum*
>* network flow problems.*
>* Function glp_maxflow_lp() is provided to convert the network flow problem to*
>* a LP which can*
>* be solved using the simplex algorithm.*
>* After the problem is solved it is necessary to map the column values back to*
>* the arcs of the*
>* network to be able to output the result.*
>* How can the columns be reliably mapped back to arcs? Using the column labels*
>* created with*
>* sprintf(name, "x[%d,%d]", a->tail->i, a->head->i);*
>* seems quite awkward.*
>* I propose glp_maxflow_lp should return a mapping table.*
All glpk network api routines use a natural ordering of arcs, which
can be explained as follows:
glp_arc *a;
int i, j;
j = 0;
for (i = 1; i <= G->nv; i++)
{ for (a = G->v[i]->out; a != NULL; a = a->t_next)
{ j++;
/* arc a corresponds to column j */
}
}