[Help-glpk] Issues / bug with glp_write_mincost

[Manish Jain]

Hello,

I am facing what seems to be like a strange issue with my use of glp_write_mincost, and have been breaking my head over it for over a day now.

I create a custom graph (i.e. i don't use glp_read_mincost but do glp_create_graph and use glp_add_vertices and glp_add_arc).

I have initialized all the arc bounds to be [0,1] and costs to be 0.

When I print this data using the below code, all the bounds and the costs are correct and as initialized.

  glp_arc* arcTmp; 

  glp_vertex* w;

  //printf("Arc bounds: %d\n", arc(arcTmp)->a_uppBndCap);

  

  for (int i=1; i<=G->nv; i++)

    {

      printf("Supply of %d: %d\n", G->v[i]->i, vertex(G->v[i])->supply);

      arcTmp = G->v[i]->out;

      for (; arcTmp != NULL;  arcTmp = arcTmp->t_next)

{

 w = arcTmp->head;

 printf("Arc Details: %d -> %d, Low: %d, Upp: %d, Cost: %f\n",G->v[i]->i, w->i, arc(arcTmp)->a_lowBndCap, arc(arcTmp)->a_uppBndCap, arc(arcTmp)->a_cost);

}

    }

arc is the #define as given in the documentation: 

#define arc(a) ((a_data *)((a)->data))

However, when I do glp_write_mincost immediately after the above code-snippet:

glp_write_mincost(G, offsetof(v_data, supply), offsetof(a_data, a_lowBndCap), offsetof(a_data, a_uppBndCap), offsetof(a_data, a_cost), fileName);

the file `fileName' has all garbled up arc costs and node supplies.

Example:

c MinCostNetworkGraph

p min 12 15

n 1 9.88131291682493e-324 <- supply should have been 2 for the first node

n 2 2.12199579096527e-314 <- supply should have been 0 for the second node

.

.

.

a 1 3 2.12199579096527e-314 4.94065645841247e-324 0 <-- lower bound is always 0 and upper bound is always 1

a 1 2 2.12199579096527e-314 4.94065645841247e-324 0

.

.

.

c eof

I tried writing down the LP by using glp_mincost_lp, but that gives the same screwed up values.

Please advise.

I can send the code files if required.

Thanks,

Manish 
University of Southern California