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<div class="moz-cite-prefix">Josh,<br>
<br>
Unable to reproduce problem with Cbc 2.8 - all tries worked fine.<br>
<br>
Would suggest upgrading as your version is nearly three years old.<br>
<br>
John Forrest<br>
On 24/09/14 12:32, Joshua Arnott wrote:<br>
</div>
<blockquote
cite="mid:CADb3=VEsSt=2AnX-hy0Umr9XYt14XivOisZNFxJjpaaBCpHmhg@mail.gmail.com"
type="cite">
<div dir="ltr">Hello,
<div><br>
</div>
<div>I've come across a MILP which CBC reports as proven
infeasible, but which GLPK solves.</div>
<div><br>
</div>
<div>I've uploaded the problem in *.lp format here:</div>
<div><a moz-do-not-send="true"
href="http://pastebin.com/EEifbfpy">http://pastebin.com/EEifbfpy</a><br>
</div>
<div><br>
</div>
<div>The problem was automatically generated based on some data.
It's one of many, and is the only one I've come across so far
that exhibits this problem. I guess it's something to do with
tolerances or precision in CBC. Is there anything I can do to
get CBC to solve it?</div>
<div><br>
</div>
<div>See below the outputs fro CBC and GLPK (via GLPSOL).</div>
<div><br>
</div>
<div>Kind regards,</div>
<div><br>
</div>
<div>Josh</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div>The output from CBC:</div>
<div>
<div><br>
</div>
<div>Welcome to the CBC MILP Solver</div>
<div>Version: 2.7.5</div>
<div>Build Date: Nov 10 2011</div>
<div>Revision Number: 1759</div>
<div><br>
</div>
<div>command line - C:\MinGW32-xy\msys\1.0\local\bin\cbc.exe
-import problem.lp -gomory on -branchAndCut (default
strategy 1)</div>
<div>Coin0009I CoinLpIO::readLp(): Maximization problem
reformulated as minimization</div>
<div>Option for gomoryCuts changed from ifmove to on</div>
<div>Continuous objective value is -4.72248e+006 - 0.00
seconds</div>
<div>Cgl0003I 0 fixed, 0 tightened bounds, 0 strengthened
rows, 23 substitutions</div>
<div>Cgl0003I 0 fixed, 0 tightened bounds, 0 strengthened
rows, 23 substitutions</div>
<div>Cgl0003I 0 fixed, 0 tightened bounds, 0 strengthened
rows, 23 substitutions</div>
<div>Cgl0003I 0 fixed, 0 tightened bounds, 0 strengthened
rows, 23 substitutions</div>
<div>Cgl0003I 0 fixed, 0 tightened bounds, 0 strengthened
rows, 23 substitutions</div>
<div>Cgl0003I 0 fixed, 0 tightened bounds, 0 strengthened
rows, 23 substitutions</div>
<div>Cgl0003I 0 fixed, 0 tightened bounds, 0 strengthened
rows, 23 substitutions</div>
<div>Cgl0003I 0 fixed, 0 tightened bounds, 0 strengthened
rows, 23 substitutions</div>
<div>Cgl0004I processed model has 23 rows, 46 columns (23
integer) and 46 elements</div>
<div>Cbc0038I Solution found of -4.72139e+006</div>
<div>Cbc0038I Before mini branch and bound, 23 integers at
bound fixed and 23 continuous</div>
<div>Cbc0038I Mini branch and bound did not improve solution
(0.01 seconds)</div>
<div>Cbc0038I After 0.01 seconds - Feasibility pump exiting
with objective of -4.72139e+006 - took 0.00 seconds</div>
<div>Cbc0012I Integer solution of -4721393.5 found by
feasibility pump after 0 iterations and 0 nodes (0.01
seconds)</div>
<div>Cbc0009I Objective coefficients multiple of 0.075</div>
<div>Cbc0001I Search completed - best objective -4721393.495,
took 0 iterations and 0 nodes (0.01 seconds)</div>
<div>Cbc0035I Maximum depth 0, 0 variables fixed on reduced
cost</div>
<div>Clp0014I Perturbing problem by 0.001 % of 0.1 - largest
nonzero change 0 (% 0) - largest zero change 0</div>
<div>Clp0006I 0 Obj -4721178 Primal inf 0.12781497 (23)</div>
<div>Clp0006I 0 Obj -4721178 Primal inf 0.12781497 (23)</div>
<div>Clp0006I 0 Obj -4721178 Primal inf 0.12781497 (23)</div>
<div>Clp0001I Primal infeasible - objective value -4721178</div>
<div>Cuts at root node changed objective from -4.72139e+006 to
-4.72139e+006</div>
<div>Probing was tried 0 times and created 0 cuts of which 0
were active after adding rounds of cuts (0.000 seconds)</div>
<div>Gomory was tried 0 times and created 0 cuts of which 0
were active after adding rounds of cuts (0.000 seconds)</div>
<div>Knapsack was tried 0 times and created 0 cuts of which 0
were active after adding rounds of cuts (0.000 seconds)</div>
<div>Clique was tried 0 times and created 0 cuts of which 0
were active after adding rounds of cuts (0.000 seconds)</div>
<div>MixedIntegerRounding2 was tried 0 times and created 0
cuts of which 0 were active after adding rounds of cuts
(0.000 seconds)</div>
<div>FlowCover was tried 0 times and created 0 cuts of which 0
were active after adding rounds of cuts (0.000 seconds)</div>
<div>TwoMirCuts was tried 0 times and created 0 cuts of which
0 were active after adding rounds of cuts (0.000 seconds)</div>
<div><br>
</div>
<div>Result - Problem proven infeasible</div>
<div><br>
</div>
<div>Objective value:
100000000000000010000000000000000000000000000000000.00000000</div>
<div>Enumerated nodes: 0</div>
<div>Total iterations: 0</div>
<div>Time (CPU seconds): 0.01</div>
<div>Time (Wallclock seconds): 0.01</div>
<div><br>
</div>
<div>Total time (CPU seconds): 0.01 (Wallclock
seconds): 0.01</div>
</div>
<div><br>
</div>
<div>And the output from GLPK:</div>
<div><br>
</div>
<div>
<div>GLPSOL: GLPK LP/MIP Solver, v4.52</div>
<div>Parameter(s) specified in the command line:</div>
<div> --cuts --lp problem.lp</div>
<div>Reading problem data from `problem.lp'...</div>
<div>117 rows, 69 columns, 184 non-zeros</div>
<div>46 integer variables, all of which are binary</div>
<div>253 lines were read</div>
<div>GLPK Integer Optimizer, v4.52</div>
<div>117 rows, 69 columns, 184 non-zeros</div>
<div>46 integer variables, all of which are binary</div>
<div>Preprocessing...</div>
<div>23 constraint coefficient(s) were reduced</div>
<div>23 rows, 46 columns, 46 non-zeros</div>
<div>23 integer variables, all of which are binary</div>
<div>Scaling...</div>
<div> A: min|aij| = 1.000e+000 max|aij| = 2.737e+003 ratio =
2.737e+003</div>
<div>GM: min|aij| = 1.000e+000 max|aij| = 1.000e+000 ratio =
1.000e+000</div>
<div>EQ: min|aij| = 1.000e+000 max|aij| = 1.000e+000 ratio =
1.000e+000</div>
<div>2N: min|aij| = 6.683e-001 max|aij| = 1.039e+000 ratio =
1.555e+000</div>
<div>Constructing initial basis...</div>
<div>Size of triangular part is 23</div>
<div>Solving LP relaxation...</div>
<div>GLPK Simplex Optimizer, v4.52</div>
<div>23 rows, 46 columns, 46 non-zeros</div>
<div>* 0: obj = 2.300000000e+001 infeas = 0.000e+000 (0)</div>
<div>* 46: obj = 4.721393495e+006 infeas = 0.000e+000 (0)</div>
<div>OPTIMAL LP SOLUTION FOUND</div>
<div>Integer optimization begins...</div>
<div>Gomory's cuts enabled</div>
<div>MIR cuts enabled</div>
<div>Cover cuts enabled</div>
<div>Clique cuts enabled</div>
<div>Constructing conflict graph...</div>
<div>No conflicts found</div>
<div>+ 46: mip = not found yet <= +inf
(1; 0)</div>
<div>+ 46: >>>>> 4.721393495e+006 <=
4.721393495e+006 0.0% (1; 0)</div>
<div>+ 46: mip = 4.721393495e+006 <= tree is empty
0.0% (0; 1)</div>
<div>INTEGER OPTIMAL SOLUTION FOUND</div>
<div>Time used: 0.0 secs</div>
<div>Memory used: 0.1 Mb (98120 bytes)</div>
</div>
</div>
<br>
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<br>
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</blockquote>
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