[Cbc] bug in Cbc-2.9.0?

[Klaus Lux]

Hi,
i would like to report a  Cbc run, which returns different answers 
according to whether I use cbc-2.8.5 or cbc.-2.9.0:
I have attched  the (input) mps file  to this email.
running cbc on cbc290bug.mps by typing

import cbc290bug.mps
solve

i get iwith cbc version 2.8.5 an objective vlue of 33 (which seems to be 
correct)
and with cbc version 2.9.0 an objective value of 34.
Kind regards,
Klaus Lux.
:
Welcome to the CBC MILP Solver
Version: 2.8.5
Build Date: Feb  8 2015

CoinSolver takes input from arguments ( - switches to stdin)
Enter ? for list of commands or help
Coin:At line 1 NAME MOC
At line 2 ROWS
At line 114 COLUMNS
At line 355 RHS
At line 405 BOUNDS
At line 418 ENDATA
Problem MOC has 110 rows, 12 columns and 464 elements
Coin0008I MOC read with 0 errors
Coin:Continuous objective value is 29 - 0.00 seconds
Cgl0003I 0 fixed, 1 tightened bounds, 1 strengthened rows, 0 substitutions
Cgl0003I 0 fixed, 0 tightened bounds, 1 strengthened rows, 0 substitutions
Cgl0004I processed model has 53 rows, 11 columns (11 integer) and 302 
elements
Cutoff increment increased from 1e-05 to 0.9999
Cbc0012I Integer solution of 42 found by DiveCoefficient after 0 
iterations and 0 nodes (0.00 seconds)
Cbc0038I Full problem 53 rows 11 columns, reduced to 13 rows 6 columns
Cbc0012I Integer solution of 35 found by RINS after 0 iterations and 0 
nodes (0.00 seconds)
Cbc0038I Full problem 53 rows 11 columns, reduced to 13 rows 6 columns
Cbc0012I Integer solution of 33 found by DiveCoefficient after 1 
iterations and 0 nodes (0.00 seconds)
Cbc0038I Full problem 53 rows 11 columns, reduced to 18 rows 7 columns
Cbc0031I 1 added rows had average density of 3
Cbc0013I At root node, 1 cuts changed objective from 29 to 33 in 3 passes
Cbc0014I Cut generator 0 (Probing) - 0 row cuts average 0.0 elements, 8 
column cuts (8 active)  in 0.000 seconds - new frequency is 1
Cbc0014I Cut generator 1 (Gomory) - 3 row cuts average 4.7 elements, 0 
column cuts (1 active)  in 0.000 seconds - new frequency is 1
Cbc0014I Cut generator 2 (Knapsack) - 0 row cuts average 0.0 elements, 0 
column cuts (0 active)  in 0.000 seconds - new frequency is -100
Cbc0014I Cut generator 3 (Clique) - 0 row cuts average 0.0 elements, 0 
column cuts (0 active)  in 0.000 seconds - new frequency is -100
Cbc0014I Cut generator 4 (MixedIntegerRounding2) - 0 row cuts average 
0.0 elements, 0 column cuts (0 active)  in 0.000 seconds - new frequency 
is -100
Cbc0014I Cut generator 6 (TwoMirCuts) - 2 row cuts average 3.5 elements, 
0 column cuts (0 active)  in 0.000 seconds - new frequency is 1
Cbc0001I Search completed - best objective 33.00000000000001, took 1 
iterations and 0 nodes (0.01 seconds)
Cbc0035I Maximum depth 0, 2 variables fixed on reduced cost
Cuts at root node changed objective from 29 to 33
Probing was tried 3 times and created 8 cuts of which 0 were active 
after adding rounds of cuts (0.000 seconds)
Gomory was tried 3 times and created 3 cuts of which 1 were active after 
adding rounds of cuts (0.000 seconds)
Knapsack was tried 3 times and created 0 cuts of which 0 were active 
after adding rounds of cuts (0.000 seconds)
Clique was tried 3 times and created 0 cuts of which 0 were active after 
adding rounds of cuts (0.000 seconds)
MixedIntegerRounding2 was tried 3 times and created 0 cuts of which 0 
were active after adding rounds of cuts (0.000 seconds)
FlowCover was tried 1 times and created 0 cuts of which 0 were active 
after adding rounds of cuts (0.000 seconds)
TwoMirCuts was tried 3 times and created 2 cuts of which 0 were active 
after adding rounds of cuts (0.000 seconds)

Result - Optimal solution found

Objective value:                33.00000000
Enumerated nodes:               0
Total iterations:               1
Time (CPU seconds):             0.01
Time (Wallclock seconds):       0.01



but wiith cbc-2.9.0 I get:Welcome to the CBC MILP Solver
Version: 2.9.0
Build Date: Jan 31 2015

CoinSolver takes input from arguments ( - switches to stdin)
Enter ? for list of commands or help
Coin:At line 1 NAME          MOC
At line 2 ROWS
At line 114 COLUMNS
At line 355 RHS
At line 405 BOUNDS
At line 418 ENDATA
Problem MOC has 110 rows, 12 columns and 464 elements
Coin0008I MOC read with 0 errors
Coin:Continuous objective value is 29 - 0.00 seconds
Cgl0003I 0 fixed, 1 tightened bounds, 1 strengthened rows, 0 substitutions
Cgl0003I 0 fixed, 0 tightened bounds, 1 strengthened rows, 0 substitutions
Cgl0004I processed model has 37 rows, 11 columns (11 integer (1 of which 
binary)) and 250 elements
Cutoff increment increased from 1e-05 to 0.9999
Cbc0012I Integer solution of 42 found by DiveCoefficient after 0 
iterations and 0 nodes (0.00 seconds)
Cbc0038I Full problem 37 rows 11 columns, reduced to 13 rows 6 columns
Cbc0012I Integer solution of 35 found by RINS after 0 iterations and 0 
nodes (0.00 seconds)
Cbc0012I Integer solution of 34 found by DiveCoefficient after 4 
iterations and 0 nodes (0.00 seconds)
Cbc0031I 1 added rows had average density of 3
Cbc0013I At root node, 1 cuts changed objective from 29 to 34 in 3 passes
Cbc0014I Cut generator 0 (Probing) - 0 row cuts average 0.0 elements, 7 
column cuts (7 active)  in 0.000 seconds - new frequency is 1
Cbc0014I Cut generator 1 (Gomory) - 3 row cuts average 4.7 elements, 0 
column cuts (0 active)  in 0.000 seconds - new frequency is 1
Cbc0014I Cut generator 2 (Knapsack) - 0 row cuts average 0.0 elements, 0 
column cuts (0 active)  in 0.000 seconds - new frequency is -100
Cbc0014I Cut generator 3 (Clique) - 0 row cuts average 0.0 elements, 0 
column cuts (0 active)  in 0.000 seconds - new frequency is -100
Cbc0014I Cut generator 4 (MixedIntegerRounding2) - 0 row cuts average 
0.0 elements, 0 column cuts (0 active)  in 0.000 seconds - new frequency 
is -100
Cbc0014I Cut generator 5 (FlowCover) - 0 row cuts average 0.0 elements, 
0 column cuts (0 active)  in 0.000 seconds - new frequency is -100
Cbc0014I Cut generator 6 (TwoMirCuts) - 2 row cuts average 3.5 elements, 
0 column cuts (0 active)  in 0.000 seconds - new frequency is 1
Cbc0001I Search completed - best objective 34, took 4 iterations and 0 
nodes (0.00 seconds)
Cbc0035I Maximum depth 0, 2 variables fixed on reduced cost
Cuts at root node changed objective from 29 to 34
Probing was tried 3 times and created 7 cuts of which 0 were active 
after adding rounds of cuts (0.000 seconds)
Gomory was tried 3 times and created 3 cuts of which 0 were active after 
adding rounds of cuts (0.000 seconds)
Knapsack was tried 3 times and created 0 cuts of which 0 were active 
after adding rounds of cuts (0.000 seconds)
Clique was tried 3 times and created 0 cuts of which 0 were active after 
adding rounds of cuts (0.000 seconds)
MixedIntegerRounding2 was tried 3 times and created 0 cuts of which 0 
were active after adding rounds of cuts (0.000 seconds)
FlowCover was tried 3 times and created 0 cuts of which 0 were active 
after adding rounds of cuts (0.000 seconds)
TwoMirCuts was tried 3 times and created 2 cuts of which 0 were active 
after adding rounds of cuts (0.000 seconds)

Result - Optimal solution found

Objective value:                34.00000000
Enumerated nodes:               0
Total iterations:               4
Time (CPU seconds):             0.01
Time (Wallclock seconds):       0.01

Coin:Total time (CPU seconds):       0.01   (Wallclock seconds):       0.02




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