[Cbc] cbc-generic is an illusion

[Lou Hafer]

Thomas, Ted,

	cbc-generic is an illusion.  This is my attempt to try and maintain
generic solver capability in cbc.  Unfortunately, it would become broken on a
regular basis due to changes to the main cbc code base and I have not had time
over the past year or so to properly maintain it.  I believe that it is
currently broken (it will compile but will crash during its unit test). You
have to specifically enable the build with
  --enable-cbc-generic
and then choose a solver with
  --with-cbc-generic-solver=xxxx
The only solvers cbc-generic has ever been tested with are clp, dylp, and glpk.
Looking at CbcGenSolvers.cpp, it looks like I might have tested with cplex 
(cpx). Can't think why I coded in Mosek (msk), as I don't have the libraries.
Code files for cbc-generic start with `CbcGen'.

	Ted, I don't have the log or other information, but I believe you're
correct.  The presence/absence of OsiXpr is completely irrelevant to a cbc
build.  It will use OsiClp (as well as lower-level classes specific to clp), and
there's nothing you can do about it.  You'll notice that the section of
Makefile.am that builds the cbc main program is conditional on the presence of
clp.

	Thomas, if what you're actually doing is coming in through OsiCbc,
specifying OsiXpr as the underlying solver, it may or may not work, depending on
the problem.  And the previous paragraph applies.  Lots of activities in libCbc
will not work because they're coded specifically for clp, at a level at or below
the Osi interface.  I'll also add that running Cbc through OsiCbc is a lot like
doing brain surgery while wearing boxing gloves.  You don't have the fine
control.

	Hence our requests for more information.  For myself, it's a case where
I haven't been able to do serious work on cbc for a while and I didn't want to
make assertions when the capabilities of the code had possibly changed.  But I
think it's highly unlikely that you're getting the build you think you're
getting.

							Lou