[Cbc] Using hotstarting functionality with modifications

[Ed Bulog]

Thank you for your responses.
Could anyone provide an example of how to correctly use solution information
when adding/removing columns and then resolving? Does my general approach
make sense or can hotstarting not be used for this purpose?
Thanks again,
Ed

On 28 July 2010 11:18, Haroldo Santos <haroldo.santos at gmail.com> wrote:

> Thanks
>
> On Tue, Jul 27, 2010 at 7:06 PM, Gabrielle A. Grun <grun at cs.sfu.ca> wrote:
> >  Hi Haroldo and Ed,
> >
> > In order the disable storing branching, I think that
> > model.setNumberBeforeTrust(0); has to be in place too i.e.
> > numberBeforeTrust_ has to be 0 as well.
> >
> > Take care.
> >
> > Gabrielle
> >
> >
> > ----- Original Message -----
> > From: Haroldo Santos
> > To: Ed Bulog
> > Cc: cbc at list.coin-or.org
> > Sent: Monday, July 26, 2010 3:20 PM
> > Subject: Re: [Cbc] Using hotstarting functionality with modifications
> > Hi Ed,
> >
> > I think that at the start of the MIP search there are some very
> > expensive routines which do not use any information of previous
> > solutions.
> >
> > In particular, doing strong branching is very expensive.
> >
> > If you want to speed up the restart, perhaps one useful option would
> > be to disable strong branching.
> >
> > setNumberStrong( 0 )
> >
> >
> > On Mon, Jul 26, 2010 at 7:04 PM, Ed Bulog <ebul014 at aucklanduni.ac.nz>
> wrote:
> >> Dear All,
> >>
> >> I have a large IP which I will be modifying constantly (by
> adding/removing
> >> coulmns) and resolving after each modification. I am trying to see if
> >> there
> >> is some way I could re-use the previous solution to make each solve
> >> faster.
> >> The obvious problem is that by adding and removing columns each time I
> >> have
> >> no way of guaranteeing that the previous solution will still be
> feasible,
> >> let alone optimal.
> >>
> >> I have experimented with the cbc example files (mostly hotstart.cpp,
> >> modify.cpp and repeat.cpp). It would be ideal if I could solve the
> >> problem,
> >> modify it and then re-use the previous solution in a hotstart. My basic
> >> approach is:
> >> - call model.initialSolve()
> >> - call model.branchandbound()
> >> - save the bestSolution array
> >> - remove some columns from the reference solver
> >> - add some columns to the reference solver
> >> - modify the bestSolution array accordingly (i.e. remove entries
> >> corresponding to deleted columns and add zeros for new columns)
> >> - call model.resetToReferenceSolver()
> >> - call model.setHotstartSolution(
> >> bestSolution)
> >> - resolve using model.branchandbound()
> >>
> >> However, this approach does not seem to do anything particularly useful.
> >> branchandbound() does not appear to do anything differently from what it
> >> does when I do not use the hotstart solution.
> >>
> >> Does 'hotstarting' only work if the model remains unchanged (as in
> >> hotstart.cpp)? Does anyone have any other suggestions? Your help is
> >> greatly
> >> appreciated.
> >>
> >> Thank you for your time,
> >>
> >> Ed
> >>
> >> _______________________________________________
> >> Cbc mailing list
> >> Cbc at list.coin-or.org
> >> http://list.coin-or.org/mailman/listinfo/cbc
> >>
> >>
> >
> >
> >
> > --
> > =============================================================
> > Haroldo Gambini Santos
> > Computing Department - Universidade Federal de Ouro Preto - UFOP
> > email: haroldo [at ] iceb.ufop.br
> > home/research page: http://www.iceb.ufop.br/decom/prof/haroldo/
> >
> > "Computer science is no more about computers than astronomy
> > is about telescopes." Edsger Dijkstra
> >
> >
> > _______________________________________________
> > Cbc mailing list
> > Cbc at list.coin-or.org
> > http://list.coin-or.org/mailman/listinfo/cbc
> >
> >
> > Gabrielle A. Grün, Ph.D. Student
> > School of Computing Science
> > Simon Fraser University
> > 8888 University Drive
> > Burnaby, BC
> > V5A 1S6
> > <http://www.cs.sfu.ca/~grun <http://www.cs.sfu.ca/%7Egrun>>
> >
> >
>
>
>
> --
> =============================================================
> Haroldo Gambini Santos
> Computing Department - Universidade Federal de Ouro Preto - UFOP
> email: haroldo [at ] iceb.ufop.br
> home/research page: http://www.iceb.ufop.br/decom/prof/haroldo/
>
> "Computer science is no more about computers than astronomy
> is about telescopes." Edsger Dijkstra
>
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