[Scip] Segmentation Fault

[Julio Rojas]

Dear all, I have been using SCIP-CLP to solve some BIP problems of my PhD
work. One of the problems has the generic form:

Min Sum(Xi)
s.t.
Xi+Xk <= 1, if Aik=1 and i<k, for i,k in {1,...,n}
Xi-Xk = 0, if {Xi,Xk} in Pj for all j in {1,...,g}, g<n
Sum(Xi)>=floor(n/2)+1
Xi in {0,1}

I know that for some setups this problem is unfeasible, but sometimes I get
segmentation fault errors like in the attached example.

I use the standalone solver. After loading it the message presented is the
following:

original problem has 75 variables (0 bin, 75 int, 0 impl, 0 cont) and 846
constraints

After presolve, the message is:

presolving:
(round 1) 69 del vars, 690 del conss, 0 chg bounds, 0 chg sides, 0 chg
coeffs, 0 upgd conss, 1046 impls, 0 clqs
(round 2) 69 del vars, 842 del conss, 0 chg bounds, 0 chg sides, 0 chg
coeffs, 0 upgd conss, 1046 impls, 0 clqs
(round 3) 69 del vars, 842 del conss, 0 chg bounds, 0 chg sides, 0 chg
coeffs, 3 upgd conss, 1046 impls, 0 clqs
(round 4) 69 del vars, 842 del conss, 0 chg bounds, 0 chg sides, 0 chg
coeffs, 4 upgd conss, 1046 impls, 0 clqs
(round 5) 70 del vars, 842 del conss, 0 chg bounds, 2 chg sides, 4 chg
coeffs, 4 upgd conss, 1056 impls, 0 clqs
(round 6) 71 del vars, 843 del conss, 0 chg bounds, 3 chg sides, 6 chg
coeffs, 4 upgd conss, 1060 impls, 0 clqs
(round 7) 71 del vars, 846 del conss, 1 chg bounds, 5 chg sides, 8 chg
coeffs, 4 upgd conss, 1062 impls, 0 clqs
(round 8) 72 del vars, 846 del conss, 1 chg bounds, 5 chg sides, 8 chg
coeffs, 4 upgd conss, 1062 impls, 0 clqs
presolving (9 rounds):
 72 deleted vars, 846 deleted constraints, 1 tightened bounds, 0 added
holes, 5 changed sides, 8 changed coefficients
 1062 implications, 0 cliques
presolved problem has 3 variables (3 bin, 0 int, 0 impl, 0 cont) and 3
constraints
      1 constraints of type <knapsack>
      2 constraints of type <logicor>
Presolving Time: 0.01

So, as you can see, the problem should be unfeasible, but when I run the
solving routine I get the following message:

 time | node  | left  |LP iter| mem |mdpt |frac |vars |cons |ccons|cols
|rows |cuts |confs|strbr|  dualbound   | primalbound  |  gap
t 0.0s|     1 |     0 |     0 | 449k|   0 |   - |   3 |   3 |   3 |   0 |
0 |   0 |   0 |   0 |      --      | 1.192662e+03 |    Inf
t 0.0s|     1 |     0 |     0 | 449k|   0 |   - |   3 |   3 |   3 |   0 |
0 |   0 |   0 |   0 |      --      | 1.170286e+03 |    Inf
Segmentation fault

Any idea on what's happening? Is there a way to avoid this problem? I'm
running the standalone solver from an R script, so I don't know if by using
C I can catch this problem. I don't program in C. Can I trust that when this
happens the solution is unfeasible? I can cope with this problem if it is
presented when the solution is unfeasible and some set of features exist in
the model.

Thank you very much for your help.
-------------------------------------------------
Julio Rojas
jcredberry at gmail.com
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