Re: [Orekit Developers] Detecting two events at the same date

[MAISONOBE Luc <luc.maisonobe@c-s.fr>]

Tanguy Yannick <Yannick.Tanguy@cnes.fr> a écrit :

> Hello,

Hi Yannick,

> We encountered some problems while trying to detect two events at  
> the same date. OREKIT propagators don't allow it, and it can lead to  
> great difficulties in some operationnal tools.
> The problem has been located in AbstractPropagator (OREKIT) because  
> events are sorted by date, and a TreeSet (occuringEvents) can only  
> store an event per date.

Good catch!

> We propose a solution to correct it, in Commons Math  
> (AbstractIntegrator) and OREKIT.
> The solution is based on a Comparator that will use a hash code to  
> arbitrary sort events when they have strictly the same date.
>
> In the method acceptStep, a TreeSet is created with a specific  
> Comparator instance :
> ****
>                 public int compare(final EventState es0, final  
> EventState es1) {
>                     int rez = orderingSign *  
> es0.getEventTime().compareTo(es1.getEventTime());
>                     if (rez == 0) {
>                         // The two event states are for the same date.
>                         // We give them an arbitrary order based on  
> the hashcode,
>                         // so that both can be kept inside a SortedSet.
>                         final int hes0 = es0.hashCode();
>                         final int hes1 = es1.hashCode();
>                         if (hes0 != hes1) {
>                             rez = hes0 > hes1 ? 1 : -1;
>                         } else {
>                             rez = 0;
>                         }
>                     }
>                     return rez;
>                 }
> ****
>
> Note : the problem is exactly the same in AbstractIntegrator  
> (Commons Math) and had been corrected the same way. Both corrections  
> give expected results.
>
> This feature is necessary for our applications. Should we create  
> JIRA tickets in Commons Math and OREKIT ?

Yes, please do and provide patches for these (including test cases).

thanks
Luc

> Best regards,
>
> Yannick



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