Re: [Help-glpk] Callbacks for column generation

[Javier Zambrano]

Thanks, another question, can you get the final branch and bound tree after the 
mip is solved?, i could add columns in each node and then add to the initial 
relaxation and re-optimize.

Regards 
Javier

2009/12/9 Andrew Makhorin <address@hidden>
> What would happen if i add cols in a callback when the reason for
> calling the calback is GLP_IROWGEN, it would start adding columns to
> the global problem?.



Currently glpk mip solver does not allow adding columns to the
current subproblem, i.e. using column generation; glp_add_cols checks
that and raises the fatal error "operation not allowed". All columns
should be added to the mip instance before a call to glp_integer.

> Could you do something like this with CPLEX?



AFAIK, cplex also does not allow generating columns during the
mip solution process. But I can mistake, so it #39;d be better to ask this
qusetion on a cplex forum.









-- 
Javier Zambrano
Thanks, another question, can you get the final branch and bound tree after the mip is solved?, i could add columns in each node and then add to the initial relaxation and re-optimize.

Regards 
Javier

2009/12/9 Andrew Makhorin <address@hidden>

> What would happen if i add cols in a callback when the reason for
> calling the calback is GLP_IROWGEN, it would start adding columns to
> the global problem?.

Currently glpk mip solver does not allow adding columns to the
current subproblem, i.e. using column generation; glp_add_cols checks
that and raises the fatal error "operation not allowed". All columns
should be added to the mip instance before a call to glp_integer.

> Could you do something like this with CPLEX?

AFAIK, cplex also does not allow generating columns during the
mip solution process. But I can mistake, so it'd be better to ask this
qusetion on a cplex forum.

-- 
Javier Zambrano