[Cbc] Documentation; Warmstart; Timelimit

[Mona Rahn]

Hi Haroldo,

Thanks for your answer.

I actually meant getting the mipstart (after solving), not entering it to
the solver. Anyway, I now programmed my own function to do that, and I feed
the solver the mipstart upon the next solve via setMIPStart as you
suggested - but it doesn't seem to change anything! When I resolve, it
still takes quite a lot of time to find a feasible solution. Do you have an
idea on that?

Thanks a lot for your help!

Kind regards,
Mona

On Wed, Nov 11, 2015 at 4:37 PM, Haroldo Gambini Santos <
haroldo.santos at gmail.com> wrote:

> 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>
> 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 Pretohttp://www.decom.ufop.br/haroldo/
>
>
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