[Cbc] Documentation; Warmstart; Timelimit

[Haroldo Gambini Santos]

Hi Mona,

To enter MIPStart programatically you should call

CbcModel  method
     void setMIPStart( const std::vector< std::pair< std::string, double 
 > > &mips ) {
        this->mipStart_ = mips;
     }

MIPstart is used when you an initial feasible solution to enter to the 
solver.

You need to inform shit solution using pairs

     variableName   value

variable names are used because the initial solution may be used in the 
pre-processed model (variable indexes change).

You only need to enter the main active decision variables. Auxiliary 
variables are computed if they exist.

Cheers,

Haroldo



On 11-11-2015 12:38, Mona Rahn wrote:
> @ John:
> Thanks for your answer.
> Is there a function to save the mipstart (as getMIPStart doesn't seem 
> to do it)? And do you have an example about mipstart?
> The event handler works perfectly btw! :) Thanks.
>
> @ Ted, Babak: thank you too!
>
> Btw, can anybody tell me is the precise difference is between
> - hotstart
> - warmstart
> - resolve
> - mipstart?
>
> Kind regards,
> Mona
>
>
> On Sat, Nov 7, 2015 at 3:46 PM, John Forrest 
> <john.forrest at fastercoin.com <mailto:john.forrest at fastercoin.com>> wrote:
>
>     Mona,
>
>     On 06/11/15 13:45, Mona Rahn wrote:
>>     Hi!
>>
>>     I have three questions:
>>
>>     1) I am pretty new in using CBC with C++. Do you have a tip on a
>>     good way to start, i.e. a documentation / tutorial / handbook for
>>     beginners? Most of the stuff I found online was aimed at a much
>>     higher level of knowledge. The documentation link that can be
>>     found on the COIN-OR website (https://projects.coin-or.org/Cbc at
>>     the bottom) doesn't work.
>>
>     Documentation has never been the strong point of Cbc.  It can be
>     useful to invoke cbc and try ? and then look at individual options
>     - see 2)
>
>>     2) I have an minimization LP that I resolve several times with
>>     different objectives. That is, I solve it, upper bound the unique
>>     variable appearing in my first objective function to the
>>     calculated value, and set another variable as my objective.
>>     Now, my question is: The solver appears to start from scratch
>>     every time I call it, but I would like to keep the old solution
>>     and start from there. Is there a way to do this? I have seen the
>>     warm start in OsiCbcSolverinterface, but I am not sure how to use it.
>>
>
>     If you do cbc and then mipstart?? you will see that you can save
>     the solution from one run and then use it as an input solution to
>     next.
>>     3) I would like to have set a time limit that only stops the
>>     program if there is already a solution found (which isn't
>>     necessarily optimal), but not if it is still searching for a
>>     solution. The only time limit I have found is
>>     CbcModel::setMaximumSeconds, but this stops the program no matter
>>     what. Do you have a solution for this?
>>
>
>     You may wish to use the drivers that allow you to call cbc as
>     normal but with changes.  Look at driver6.cpp.  If you have a
>     driver like that then you could check if you have a solution and
>     then stop on time.  I would suggest modifying
>     MyEventHandler3::event to check if event was treeStatus and
>     solution found and too many seconds.
>
>     John Forrest
>>     Thanks a lot in advance.
>>
>>     Kind regards,
>>     Mona
>>
>>
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>
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-- 
==================================================
Haroldo Gambini Santos
D.Sc, Computer Science
Universidade Federal de Ouro Preto
http://www.decom.ufop.br/haroldo/

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