basisIsAvailable and tableau operations after clone

[akazachk]

Hi all, if I clone a base solver instance (in my case, of OsiClpSolverInterface) that is proven optimal and for which basisIsAvailable returns true, the cloned solver no longer preserves this status because, at least for Clp, the copy constructor called within clone sets lastAlgorithm_ = 0.

What would be the right approach to access the tableau in the cloned solver, ensuring that it is exactly the same tableau as for the base solver instance? My guess is calling resolve on the cloned solver will typically suffice, but I want to make sure that there are no edge cases in which a different basis/tableau would be obtained. (In which case, if resolve produces a different tableau, then potentially the set of available cuts, for example, would be different, which would be problematic for creating reliable baselines.)

A snippet of the type of code that I am trying to use is below:

OsiSolverInterface* origSolver = new OsiClpSolverInterface;
origSolver = readMps("bm23.mps.gz");
origSolver->initialSolve();
// At this point, origSolver->basisIsAvailable() is true

OsiSolverInterface* copySolver = origSolver->clone();
// Here, copySolver->isProvenOptimal() is true, but copySolver->basisIsAvailable() is false

Thank you,
Aleks

[jjhforrest]

1. The basis will be identical.
2. The values in the solution may differ by an incredibly small amount. This is because of the difference between a solve that does iterations and one that is given an optimal basis. The simplest thing to do is to do a resolve on origSolver before doing anything else. Once you are happy with results then try taking out some of the resolves - or directly use ClpSimplex where you have much more control.