[Coin-discuss] setColSolution

[Brady Hunsaker]

I'm now thinking of the setColSolution issue in the broader context of
functions that aren't supported by a solver.

For example, what do solvers with no MIP routines do with
branchAndBound?  It doesn't make sense to me to have them "pretend" to
support the function (by rounding or whatever).  It seems preferable
to have them complain loudly so the user knows.  I view setColSolution
in the same light (though in that case we can add documentation that
directs users to setWarmStart).

Lou has offered a potential solution that may lead to a resolution of
setColSolution issue, but I would still like to see a general
guideline for the behavior of a solver when it doesn't support a
function.  Right now my preference is to have the solver throw an
exception so the user knows the function isn't supported. 

Brady

On Tue, Apr 29, 2003 at 10:47:05PM -0400, Matthew Saltzman wrote:

> On Tue, 29 Apr 2003, JP Fasano wrote:
> 
> > I would advocate the second option if it can reasonably be implemented.
> > If not, then the first option (which is how OsiXprSolverInterface works).
> > I don't like the third option because then an application program would
> > have to be modifed to use OsiGlpkSolverInterface.
> > In my mind this defeats the value of the Open Solver Interface.
> 
> I agree with JP's point about the third option.  IIRC (and the XPRESS
> implementation was mine), the original spec called for just setting the
> cache for solvers that could not accept setting a solution.  The reasoning
> was that the solution could be set to anything, and it was not clear (at
> least at the time) how to specify a basis to be loaded for a nonbasic
> solution.  If solvers could accept a superbasic solution as input, that
> would be something to consider, but they can't in general and you are
> still stuck trying to specify a basis to associate with the solution.
> 
----------------
Brady Hunsaker
Georgia Institute of Technology
Program in Algorithms, Combinatorics, and Optimization
School of Industrial and Systems Engineering

E-mail address:   hunsaker at isye.gatech.edu