[rules-dev] Planner: should getBestSolution() return null when there is no initialized solution?

[Geoffrey De Smet]

Op 28-06-11 11:23, Michael Anstis schreef:
> Not completely understanding why solver.solve() would only run for 1ms, 
It seems stupid indeed, but there are some cases:
- Cancellation: the user presses the "terminate early" button
- Cancellation: the whole system is going down (ctrl-c / kill)
- In real-time planning cases, the answer is needed NOW (even though we 
just started planning 1 or 10ms ago).
In that last case you'll probably still want to have an initialized 
solution and configure it appropriate to do random initialization (= 
really fast and really stupid) anyway.

So it looks like cancellation is the only real use case.
And I 'll support JBRULES-3105 "Planner: construction heuristics should 
be able to optionally ignore terminateEarly until a solution is 
initialized" in the future,
for the real-time planning case.
> isn't a partially initialised starting solution a runtime error and 
> (3) have solver.getBestSolution() throw a 
> "SolutionsNotInitialisedException" an option?
Intresting idea. It should definitely not be a checked exception. Let's 
call this 3)

> 1) It returns null. So you 'll need to do null checks:
> Solution bestSolution = solver.getBestSolution();
> if (bestSolution == null) {
>      // ... do things with bestSolution
>      Score bestScore = bestSolution.getScore();
> }
>
> 2) It returns the partially initialized solution. So you'll need to do
> isBestSolutionInitialized checks:
> Solution bestSolution = solver.getBestSolution();
> if (solver.isBestSolutionInitialized()) {
>      // ... do things with bestSolution
>      Score bestScore = bestSolution.getScore();
> }
3) it throws a SolutionUninitialisedException (runtime exception)
If you configured JBRULES-3105, then this works:
      Solution bestSolution = solver.getBestSolution();
      // ... do things with bestSolution
      Score bestScore = bestSolution.getScore();
Otherwise, you probably want to do this instead:
try {
      Solution bestSolution = solver.getBestSolution();
      // ... do things with bestSolution
      Score bestScore = bestSolution.getScore();
} catch (SolutionUninitialisedException e) {
     // ...
}
>
> On 28 June 2011 10:18, Geoffrey De Smet <ge0ffrey.spam at gmail.com 
> <mailto:ge0ffrey.spam at gmail.com>> wrote:
>
>     Normally you use Planner like this:
>
>     solver.solve()
>     Solution bestSolution = solver.getBestSolution();
>     // ... do things with bestSolution
>     Score bestScore = bestSolution.getScore();
>
>     But let's suppose we give it 1 millisecond to plan and use a big,
>     uninitialized starting solution
>     and our initialization algorithm actually terminates immediately as
>     requested.
>     It won't be able to completely initialize the solution in that case.
>     What should solver.getBestSolution() return in that case? null or the
>     partially initialized solution?
>
>     1) It returns null. So you 'll need to do null checks:
>     Solution bestSolution = solver.getBestSolution();
>     if (bestSolution == null) {
>          // ... do things with bestSolution
>          Score bestScore = bestSolution.getScore();
>     }
>
>     2) It returns the partially initialized solution. So you'll need to do
>     isBestSolutionInitialized checks:
>     Solution bestSolution = solver.getBestSolution();
>     if (solver.isBestSolutionInitialized()) {
>          // ... do things with bestSolution
>          Score bestScore = bestSolution.getScore();
>     }
>
>     What makes more sense?
>
>     --
>     With kind regards,
>     Geoffrey De Smet
>
>
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-- 
With kind regards,
Geoffrey De Smet

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