[Help-glpk] Re: need help to understand why glpk cant solve my problem

[Andrew Makhorin]

> First of all I would just like to say hello too you all and I hope I wont
> make a complete fool out of myself for writing this :)
> 
> I am trying to solve a train dispatching problem.
> I have a graph with 54 nodes and I want two trains to travel from
> different starting nodes and switch places. So basically I want train a to
> go from node i to node j and I want train b to go from node j to node i.
> I have set up a simple mathematical model to avoid collisions between the
> trains.
> 
> The error message I get from running this is the following:
> 
> spx_invert: the basis matrix is singular
> spx_simplex: numerical problems with basis matrix
> spx_simplex: sorry, basis recovery not implemented yet
> mip_driver: cannot solve current LP relaxation
> lpx_integer: cannot solve current LP relaxation
> 
> Now this is a fairly big problem and I am not sure glpk can solve it at all.
> So I am mostly trying to understand _why_ it cant solve it.
> My guess is that it just is to big, but I wanted to make sure that that is
> the case and I hope maybe one of you could confirm it or explain it to me.
> 
> If you want the acctual data and model files just say so and I will supply
> them.

Please write your model in mps format, gzip it, and post it to me
<address@hidden> . It is difficult to say what happened not seeing the
model itself.

Andrew Makhorin