[Clp-tickets] [COIN-OR Linear Programming Solver] #53: Missing pivotSequence_ initialization causes CBC crash

[COIN-OR Linear Programming Solver]

#53: Missing pivotSequence_ initialization causes CBC crash
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 Reporter:  dindy       |      Owner:  somebody
     Type:  defect      |     Status:  new
 Priority:  major       |  Milestone:
Component:  component1  |    Version:  1.0
 Keywords:              |
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 Hello,

 first of all this bug report started from this CBC one:

 https://projects.coin-or.org/Cbc/ticket/115

 I add that I tested with the latest CBC trunk, which uses CLP 1.14, and
 the problem is still there. After some debugging I think I traced down the
 problem to a missing pivotSequence_ initialization in
 ClpPrimalColumnSteepest::pivotColumn. Looking at other parts of the code
 it seems to me that setting pivotRow_ to -2 should mean that the pivot
 computation should be restarted, but this is not done in
 ClpPrimalColumnSteepest::pivotColumn. I tried adding a simple:

 if (pivotRow < -1) pivotSequence_ = -1;

 at the beginning of ClpPrimalColumnSteepest::pivotColumn, just after:

 int pivotRow = model_->pivotRow();

 and the bug has gone. BTW, I'm no expert in the simplex algorithm and the
 code is pretty complicated to me so I'm unsure if this is the best place
 to reset pivotSequence_.

 Hope it helps, and thanks for the excellent software.

 Bye,

 Denis Sbragion

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Ticket URL: <https://projects.coin-or.org/ticket/53>
COIN-OR Linear Programming Solver <http://projects.coin-or.org/Clp>
A linear programming solver.