[Cbc] Fwd: Beginner here
Patrik Dufresne
info at patrikdufresne.com
Sun Sep 15 09:18:24 EDT 2013
Hi,
Thanks everyone. Your help make me save a lot of time. I'm very thankful.
--
Patrik Dufresne Service Logiciel
http://patrikdufresne.com/
514-971-6442
438-738-1376
114 rue des Hautbois, app1
St-Colomban, QC J5K 2H6
On Thu, Sep 12, 2013 at 3:15 PM, Haroldo Gambini Santos <
haroldo.santos at gmail.com> wrote:
> On 12-09-2013 08:08, Patrik Dufresne wrote:
>
>
> Hi Haroldo,
>
> Your answer are very comprehensible. I'm very thankful to get a reply. As
> I understand, the main idea is to create the problem using
> OsiClpSolverInterface#addCol() or OsiClpSolverInterface#addRow(). Then I
> need to call OsiClpSolverInterface#initialSolve(). Questions:
>
> 1. I had a look at all the Cbc examples and it does involve the class
> CbcModel. Should I care about it?
>
> 2. As I understand, clp is used to run the simplex algorithm. Cbc is
> used to run the branch and bound. So I guess I need to run both step
> explicitly?
> OsiClpSolverInterface#initialSolve()
> CbcModel#branchAndBound()
>
> Yes. initialSolve must be called before.
> CbcModel.branchAndBound will perform a "pure" branch-and-bound (no cuts
> and heuristics). You can explicitly bind it to other Cbc classes to include
> these features (which often speed up a lot the search) or use the function
> CbcMain which will run everything using the same features as if you
> started the search from the command line. the code would look more or less
> as:
>
> CbcModel modelA(*linearProgram);
> CbcModel *model = &modelA;
> CbcMain0(modelA);
> const char * argv2[]={"problemName","-solve","-quit"};
> CbcMain1(3, argv2, modelA);
>
>
>
>
>
> 3. Reading the doc about CbcModel, it copy the solver passed in the
> constructor. What is the suggested approach if I need to reuse the problem
> over and over?
> The following is what I think I should do:
>
> Since for MIPs there is no good reoptimization technique the cost of
> creating CbcModel again will probably be small comparedto the cost of
> reoptimizing an Integer Program. But the OsiClpSolverInterface you can
> change and do not need to recreated it again, probably.
>
> a. create new instance of OsiClpSolverInterface named solver1
> b. call solver1.addCol() and solver1.addRow() to build the problem
> c. set objective value using solver1.setObjCoeff() and
> solver1.setObjSense()
> d. call solver1.initialSolve()
> e. create new instance of CbcModel(solver1) named model1
> f. call model1.branchAndBound()
> g. get the objective value model1.getObjValue()
>
> reusing the problem:
> h. call addCol() or addRow() on solver1
> i. run step c to g again
>
> The end result: I will create a single instance of OsiClpSolverInterface
> and multiple instance of CbcModel. I also sees a different approach to
> create a single CbcModel and call CbcModel.solver() to update the problem
> multiple time. I guess both would work, but what is the "faster" one. The
> one avoiding memory copy, useless recomputation etc.
>
> 4. Using the command line, I notice a performance improvement to solve
> my problem using the following arguments: cbc .. mps -feas both -doh -solve
> ... Basically, activating the feasibility pump help alot. As I understand,
> I need to create a new instance of CbcHeuristicFPump and call
> CbcModel.addHeuristic( ).
>
>
>
> --
> Patrik Dufresne Service Logiciel
> http://patrikdufresne.com/
> 514-971-6442
> 438-738-1376
> 114 rue des Hautbois, app1
> St-Colomban, QC J5K 2H6
>
>
> On Wed, Sep 11, 2013 at 8:47 PM, Haroldo Gambini Santos <
> haroldo.santos at gmail.com> wrote:
>
>> Hi Patrick,
>>
>>
>>
>> On 11-09-2013 21:23, Patrik Dufresne wrote:
>>
>> Hello,
>>
>> I'm just getting started with CoinCbc. I found the learning curve very
>> steep compare to GLPK where everything is documented in details. I'm
>> struggling with all the object available to create a model and solve it. To
>> avoid any beginner mistake, I'm asking the mailing list in hope to get tips
>> for my very specific needs.
>>
>> 1. If I want to create a representation of my problem using
>> variables(columns) and constraints(rows), should I use the OsiClpSolverInterface
>> or CoinModel?
>>
>> *OsiClpSolverInterface* - this class inherits from OsiSolverInterface
>> so that any method you use to create/modify your problem will be compatible
>> with other Osi Interfaces (e.g.: cplex
>> by using OsiCpxSolverInterface)
>>
>> http://www.coin-or.org/Doxygen/Osi/classOsiSolverInterface.html
>>
>>
>>
>> 2. If I need to do subsequent modification to the problem (e.g.: adding
>> variables or constraints), can I reuse the same object over and over again?
>>
>> *Yes*
>>
>> Basically, I need to create a problem. Solve it. Add a new constraint.
>> Solve it. etc. etc. A snippet would be very welcome.
>>
>> I do not have a small code here, but basically what you need to do is:
>>
>> create an OsiClpSolverInterface
>>
>> after that you can cast the object to an OsiSolverInterface pointer, so
>> that all your calls will be solver independent (not required)
>>
>> to create your problem:
>> use methods
>>
>> addCol/addCols, addRow/addRows
>>
>> you can also use a CoinBuild object to to create and populate constraints
>> (I think this is easier) :
>> http://www.coin-or.org/Doxygen/CoinAll/class_coin_build.html
>>
>> basically you add rows to a CoinBuild object and then add this object to
>> OsiSolverInterface
>>
>> after your problem is built you can call initialSolve to solve the
>> LP
>>
>> Cheers
>>
>>
>> Thanks
>>
>> --
>> Patrik Dufresne Service Logiciel
>> http://patrikdufresne.com/
>> 514-971-6442
>> 438-738-1376
>> 114 rue des Hautbois, app1
>> St-Colomban, QC J5K 2H6
>>
>>
>> _______________________________________________
>> Cbc mailing listCbc at list.coin-or.orghttp://list.coin-or.org/mailman/listinfo/cbc
>>
>>
>> --
>> ==================================================
>> Haroldo Gambini Santos
>> D.Sc, Computer Science
>> Universidade Federal de Ouro Pretohttp://www.decom.ufop.br/haroldo/
>>
>>
>
>
>
> _______________________________________________
> Cbc mailing listCbc at list.coin-or.orghttp://list.coin-or.org/mailman/listinfo/cbc
>
>
> --
> ==================================================
> Haroldo Gambini Santos
> D.Sc, Computer Science
> Universidade Federal de Ouro Pretohttp://www.decom.ufop.br/haroldo/
>
>
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