[Clp] Regression with the current trunk.

[John Forrest]

Not quite sure what bug you are reporting.

I have not repeated your experiments but when I run that problem using 
clp I get x13 with value of 0 and objective of -400.  Using cbc without 
preprocessing I get x13 with value of 0 and objective of -400.  If I use 
preprocessing x13 is 1 but the objective is still -400.  Your output 
shows that x13 has a reduced cost of 0 so either 0 or 1 is valid.  I 
presume the changes to presolve flipped a coin a different way.

If you are just using clp then an error in presolve is self correcting 
as after solving and postsolving it checks optimality. It looks to me as 
if changes in code are leading to alternate optima - but that may happen 
with any changes - maybe not so often with such a tiny problem.

It is quite possible a bug was introduced by the changes, but that would 
probably show up with cbc - not clp.

Regards

John Forrest


On 14/08/14 09:04, ycollette.nospam at free.fr wrote:
> Hello,
>
> I finally found the good set of options for the clp executable.
>
> First, I checkout the Cbc trunk.
> Then, I cd into CoinUtils directory and do a 'svn up -r 1698'
> Then, I cd into the main trunk directory:
> ./configure --enable-aboca=2 --prefix=/opt/cbc-devel-ok LDFLAGS=-lpthread
> make
> make install
>
> Then, I cd into CoinUtils directory and do a 'svn up'
> Then, I cd into the main trunk directory:
> ./configure --enable-aboca=2 --prefix=/opt/cbc-devel-nok LDFLAGS=-lpthread
> make clean
> make
> make install
>
> For my tests, I use the attached lp file.
>
> In a first terminal:
> export LD_LIBRARY_PATH=/opt/cbc-devel-nok/lib:$LD_LIBRARY_PATH
> /opt/cbc-devel-nok/bin/clp Coin_1.lp -abc on -dualS on -solution Coin_1_nok.sol -solve
>
> In a second terminal:
> export LD_LIBRARY_PATH=/opt/cbc-devel-ok/lib:$LD_LIBRARY_PATH
> /opt/cbc-devel-ok/bin/clp Coin_1.lp -abc on -dualS on -solution Coin_1_ok.sol -solve
>
> diff Coin_1_ok.sol Coin_1_nok.sol
> 18c18
> <      15 x13                    0                       0
> ---
>>       15 x13                    1                       0
> By the way, under fedora 21 64 bits, I needed to add LDFLAGS=-lpthread to allow executables to be built.
>
> Best regards,
>
> YC
>
>
>