On 01/17/2013 08:24 PM, Gilles Sadowski wrote: >>> [...] >>> >>> If we do not have the resources to dig further into the real problem, we can >>> circumscribe it by indicating which interval of epsilon values are >>> considered trustworthy (and declining all resposibility if user try pushing >>> the implementation too far). >> >> Well, I do disagree. >> I do not want to have a situation where users get different results with >> each run. I want to have deterministic behavior for deterministic >> algorithms. > > Do you suggest that the JVM algorithm is not deterministic? ;-)
The iteration order of HashSet entries is based on the hash code of the entries and the number of buckets in the underlying HashMap. As the hash code of a LinearConstraint is derived from its values (including an enum - Relationship) it may change, and in fact does (the enum has no overridden hashCode method, and Java 6+ does not seem to guarantee the same hashCode for the same enum every time contrary to what Java 5 seems to do). So every time you run, your iteration order could be different (and you can see it with the test case). >> Yes, there are numerical stability issues, which in this case can be >> treated by relaxing the convergence criteria as the user did. > > Then, I propose that lower bound of the convergence criterion be set as a > precondition and the algorithm will be deterministic in a more obvious way. > >> Otoh, we should have thorough testing where a permutation of the linear >> constraints could be a useful addition to detect more such issues. For >> such a flexible tool like the SimplexSolver, there will always be >> problems where the solution is difficult to find, and will require some >> tuning. Even octave (using the very good and mature glpk library) did >> not find the optimal solution in this case. > > This even further convinces me that we should not change an implementation > detail: such details simply must not have visible side-effects. > It has a visible effect here because the precondition is not satisfied. I do not fully understand, about which precondition do we talk here? Thomas --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
