[Cbc] Fwd: Beginner here
Haroldo Gambini Santos
haroldo.santos at gmail.com
Thu Sep 12 15:15:53 EDT 2013
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 <http://patrikdufresne.com/>/
> 514-971-6442 <tel:514-971-6442>
> 438-738-1376 <tel: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 <mailto: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 <http://patrikdufresne.com/>/
>> 514-971-6442 <tel:514-971-6442>
>> 438-738-1376 <tel:438-738-1376>
>> 114 rue des Hautbois, app1
>> St-Colomban, QC J5K 2H6
>>
>>
>> _______________________________________________
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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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> http://list.coin-or.org/mailman/listinfo/cbc
--
==================================================
Haroldo Gambini Santos
D.Sc, Computer Science
Universidade Federal de Ouro Preto
http://www.decom.ufop.br/haroldo/
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