[Couenne] couenne optimal result is inferior than my heuristic?

[renan maglasang]

Hello to you Pietro, and to all members.

Any help would mean a lot. I itemized my questions so you can address it
separately.
I copied the couenne result below for your reference.

QUESTIONS:

Question 1.
-the heuristic i used can find a better result which is

facings:
1-4
2-3
3-1
4-1
5-15
6-9
profit = 1807.64

-(although the profit difference is slight but the bigger the better and
the variable values are different too)
-i checked capacity capacity of both solution, its okay both are 164 which
are less than max of 166

Question 2.
-i found some solution by couenne which violates the constraints too, it
says optimal but when i try to manually compute, capacity constraint is
violated.

Question 3.
This warning below...does this have something to do with all these
discrepancies of couenne results?
Error in an AMPL evaluation. Run with "halt_on_ampl_error yes" to see
details.



_____________________________________________________________________________________________________

ampl: model irion.txt;

ampl: data bulb.txt;

ampl: option solver couenne;

ampl: solve;

couenne:

ANALYSIS TEST: Problem size before reformulation: 12 variables (12
integer), 1 constraints.

Problem size after  reformulation: 109 variables (19 integer), 1
constraints.



******************************************************************************

This program contains Ipopt, a library for large-scale nonlinear
optimization.

 Ipopt is released as open source code under the Common Public License
(CPL).

         For more information visit http://projects.coin-or.org/Ipopt

******************************************************************************



NOTE: You are using Ipopt by default with the MUMPS linear solver.

      Other linear solvers might be more efficient (see Ipopt
documentation).





Error in an AMPL evaluation. Run with "halt_on_ampl_error yes" to see
details.

Cbc0012I Integer solution of -1807.27 found by Init Rounding NLP after 0
iterations and 0 nodes (0.00 seconds)

Cbc0031I 30 added rows had average density of 2

Cbc0013I At root node, 30 cuts changed objective from -9.99e+012 to
-9.99e+012 in 13 passes

Cbc0014I Cut generator 0 (Couenne convexifier cuts) - 327 row cuts average
2.0 elements, 16 column cuts (46 active)

Cbc0010I After 0 nodes, 1 on tree, -1807.27 best solution, best possible
-9.99e+012 (0.09 seconds)

Cbc0010I After 100 nodes, 19 on tree, -1807.27 best solution, best possible
-9.99e+012 (1.25 seconds)

Cbc0010I After 200 nodes, 28 on tree, -1807.27 best solution, best possible
-9.99e+012 (1.50 seconds)

……………………….(I deleted some parts to make it shorter)

Cbc0010I After 58600 nodes, 163 on tree, -1807.27 best solution, best
possible -1834.51 (90.14 seconds)

Cbc0010I After 58700 nodes, 127 on tree, -1807.27 best solution, best
possible -1832.28 (90.25 seconds)

Cbc0010I After 58800 nodes, 92 on tree, -1807.27 best solution, best
possible -1829.64 (90.37 seconds)

Cbc0010I After 58900 nodes, 51 on tree, -1807.27 best solution, best
possible -1825.32 (90.48 seconds)

Cbc0010I After 59000 nodes, 14 on tree, -1807.27 best solution, best
possible -1819.16 (90.62 seconds)

Cbc0001I Search completed - best objective -1807.268742209032, took 520060
iterations and 59028 nodes (90.64 seconds)

Cbc0035I Maximum depth 121, 1253 variables fixed on reduced cost

 Couenne convexifier cuts was tried 94303 times and created 1520652 cuts of
which 138882 were active after adding rounds

                "Finished"



couenne: Optimal

ampl: display facings;

facings [*] :=

1   4

2   2

3   1

4   1

5  15

6  10

;

ampl: display profit;

profit = 1807.27
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://list.coin-or.org/pipermail/couenne/attachments/20150715/b553e5c2/attachment.html>