[Cbc] cplex (optimal) vs cbc (infeasible or unbounded)

[Haroldo Santos]

Just to provide the result of another solver:

GLPK 4.39 quickly says that the problem is UNBOUNDED  :

glpsol --cpxlp --intopt --cuts subProb.n0.c0.p3.b2.lp
GLPSOL: GLPK LP/MIP Solver 4.39
Reading problem data from `subProb.n0.c0.p3.b2.lp'...
293 rows, 861 columns, 665 non-zeros
366 integer variables, 60 of which are binary
1337 lines were read
ipp_basic_tech:  0 row(s) and 720 column(s) removed
ipp_reduce_bnds: 2 pass(es) made, 80 bound(s) reduced
ipp_basic_tech:  0 row(s) and 0 column(s) removed
ipp_reduce_coef: 1 pass(es) made, 0 coefficient(s) reduced
glp_intopt: presolved MIP has 293 rows, 141 columns, 665 non-zeros
glp_intopt: 61 integer columns, 60 of which are binary
Scaling...
 A: min|aij| =  1.670e-01  max|aij| =  1.250e+02  ratio =  7.485e+02
GM: min|aij| =  1.275e-01  max|aij| =  7.845e+00  ratio =  6.155e+01
EQ: min|aij| =  1.625e-02  max|aij| =  1.000e+00  ratio =  6.155e+01
2N: min|aij| =  1.044e-02  max|aij| =  1.604e+00  ratio =  1.537e+02
Constructing initial basis...
Size of triangular part = 293
Solving LP relaxation...
*     0: obj =   0.000000000e+00  infeas =  0.000e+00 (0)
*     2: obj =   0.000000000e+00  infeas =  0.000e+00 (0)
PROBLEM HAS UNBOUNDED SOLUTION
Time used:   0.0 secs
Memory used: 0.5 Mb (510288 bytes)


On Thu, Jul 30, 2009 at 11:34 PM, Matthew Galati <magh at lehigh.edu> wrote:

> Cplex and CBC are giving completely different results on this one. I don't
> think this problem is infeasible or unbounded - so I think it might be a CBC
> bug.
>
> http://coral.ie.lehigh.edu/~magh/tmp/subProb.n0.c0.p3.b2.lp<http://coral.ie.lehigh.edu/%7Emagh/tmp/subProb.n0.c0.p3.b2.lp>
>
>
>
> Problem 'subProb.n0.c0.p3.b2.lp' read.
> Read time =    0.00 sec.
> CPLEX> opt
> Tried aggregator 1 time.
> MIP Presolve eliminated 290 rows and 843 columns.
> Reduced MIP has 3 rows, 3 columns, and 6 nonzeros.
> Presolve time =    0.00 sec.
> Clique table members: 1.
> MIP emphasis: balance optimality and feasibility.
> Root relaxation solution time =    0.00 sec.
>
> MIP - Integer optimal solution:  Objective = -7.4380291900e+03
> Solution time =    0.00 sec.  Iterations = 0  Nodes = 0
>
>
>
>
>
>
>
> Coin Cbc and Clp Solver version 2.30.00, build Dec  1 2008
> command line - ./bin/cbc /users/magala/subProb.n0.c0.p3.b2.lp (default
> strategy 1)
> ### WARNING: CoinLpIO::readLp(): Variable x(1) does not appear in objective
> function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(7) does not appear in objective
> function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(133) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(139) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(145) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(151) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(157) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(163) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(169) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(175) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(393) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(396) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(409) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(472) does not appear in
> objective function or constraints
> ### WARNING: CoinLpIO::readLp(): Variable x(487) does not appear in
> objective function or constraints
> Coin0508I Presolve thinks problem is unbounded
> Continuous objective value is -1.16003e+14 - 0.00 seconds
> Coin0508I Presolve thinks problem is unbounded
> Cgl0000I Cut generators found to be infeasible!
> Pre-processing says infeasible or unbounded
> Total time 0.02
>
>
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>
>


-- 
=============================================================
Haroldo Gambini Santos
Computing Department - Universidade Federal de Ouro Preto - UFOP
email: haroldo.santos at gmail.com
home/research page:  http://www.ic.uff.br/~hsantos/

“BE the change you want to see in the world” -Mahatma Gandhi
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