[Clp] CLP versus GLPK versus CPLEX

[Victor Miller]

I have a number of fairly large LP problems for which I just want to find
any feasible solution.  I've given these problems to GLPK, CLP and CPLEX
"out of the box" (i.e. not specifying any parameters, just asking for the
default behavior).  Although all of them do find the feasible vectors that I
desired, only CLP produces "nice" vectors.  For instance one of the problems
has 32768 variables divided into two sets of 16384.  CLP produces a vector
for which only 3 out of the 16384 variables in the first set are nonzero,
and all the nonzero values for variables in the second set are 1.0 and all
of the nonzero indices occur in consecutive chunks of 256.  My question is
what is the default solution strategy for CLP (and if anyone knows for GLPK
and CPLEX).  Clearly, by serendipity, CLP is finding some nice structure in
my problem, so I'd like to uncover it.

Victor Miller
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