[Cbc] -extraVariables success and failure

[acw at ascent.com]

Thank you, Stefan and John, for the svn URL for the trunk sources.

The good news: I built Cbc successfully, and using -extraVariables, the 
new executable was able to solve that troublesome problem in less than 5 
CPU seconds.  The trick of aggregating variables with identical costs is 
very, very effective on our typical problems.

The bad news is that -extraVariables does not seem to play well with 
-threads.  Perhaps we will not need -threads, if -extraVariables helps us 
so much, but I figured you would want to see the result, so I've appended 
a log below.  It finds a preliminary solution with DiveCoefficient, then 
works all its root cuts, but then it segfaults instantly.

We will be excitedly playing with -extraVariables, and if it works as well 
as it promises to on our usual problems, we won't miss multithreading for 
a while, so the priority on this is quite low.  Thank you, John, for the 
spectacular improvement (something like 8 orders of magnitude on this 
problem)!

Allan Wechsler
(Cbc log below.)

[acw at ARVON coin-Cbc]$ bin/cbc ../last-problem.mps -extrav 8 -threads 104 
-solve
Welcome to the CBC MILP Solver 
Version: Trunk (unstable) 
Build Date: Mar 20 2013 
Revision Number: 1876 

command line - bin/cbc ../last-problem.mps -extrav 8 -threads 104 -solve 
(default strategy 1)
At line 1 NAME          BLANK
At line 2 ROWS
At line 1694 COLUMNS
At line 7264 RHS
At line 7664 BOUNDS
At line 7883 ENDATA
Problem BLANK has 1690 rows, 218 columns and 10834 elements
Coin0008I BLANK read with 0 errors
extraVariables was changed from 0 to 8
threads was changed from 0 to 104
Continuous objective value is 496912 - 0.01 seconds
Cgl0003I 0 fixed, 35 tightened bounds, 2 strengthened rows, 0 
substitutions
Cgl0004I processed model has 346 rows, 218 columns (218 integer) and 2983 
elements
Problem has 218 integers (0 of which binary) and 0 continuous
218 integer have nonzero objective, 0 have zero objective, 8 different 
nonzero (taking abs)
48 variables have objective of 1
1 variables have objective of 4
28 variables have objective of 16.29
28 variables have objective of 31.58
8 variables have objective of 233.333
35 variables have objective of 1235.43
35 variables have objective of 1430.12
35 variables have objective of 2441.3
Replacing model - 7 new variables
Cbc0012I Integer solution of 594089.87 found by DiveCoefficient after 0 
iterations and 0 nodes (0.19 seconds)
Cbc0038I Full problem 353 rows 225 columns, reduced to 307 rows 135 
columns - too large
Cbc0031I 11 added rows had average density of 185.27273
Cbc0013I At root node, 11 cuts changed objective from 497140.24 to 
499066.93 in 100 passes
Cbc0014I Cut generator 0 (Probing) - 0 row cuts average 0.0 elements, 4 
column cuts (4 active)  in 0.768 seconds - new frequency is 1
Cbc0014I Cut generator 1 (Gomory) - 1621 row cuts average 213.4 elements, 
0 column cuts (11 active)  in 0.561 seconds - new frequency is 1
Cbc0014I Cut generator 2 (Knapsack) - 0 row cuts average 0.0 elements, 0 
column cuts (0 active)  in 0.045 seconds - new frequency is -100
Cbc0014I Cut generator 3 (Clique) - 0 row cuts average 0.0 elements, 0 
column cuts (0 active)  in 0.001 seconds - new frequency is -100
Cbc0014I Cut generator 4 (MixedIntegerRounding2) - 0 row cuts average 0.0 
elements, 0 column cuts (0 active)  in 0.106 seconds - new frequency is 
-100
Cbc0014I Cut generator 5 (FlowCover) - 0 row cuts average 0.0 elements, 0 
column cuts (0 active)  in 0.235 seconds - new frequency is -100
Cbc0014I Cut generator 6 (TwoMirCuts) - 225 row cuts average 165.6 
elements, 0 column cuts (0 active)  in 0.143 seconds - new frequency is 
-100
Segmentation fault (core dumped)
[acw at ARVON coin-Cbc]$ 
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