[Orekit Developers] Changing conditions to a tolerance

[Hank Grabowski <hank@applieddefense.com>]

During some V&V tests I was running when I tried to get the tolerance of a computation down to millisecond or very tight levels I sometimes ran into a condition where the root finder in the propagators went a bit haywire (it says it doesn't have roots in the interval).  A way we were able to get past this for testing purposes were changes as follows to orekit/propagation/events/EventState.java:

Changed assert comparison on line 266

OLD check(ga == 0.0 || gb == 0.0 || (ga > 0.0 && gb < 0.0) || (ga < 0.0 && gb > 0.0));

NEW check(equalsWithinTolerance(ga, 0.0) || equalsWithinTolerance(gb, 0.0) || (ga > 0.0 && gb < 0.0) || (ga < 0.0 && gb > 0.0));

Changed assert comparison on line 386

OLD check(increasing == gb >= ga);

NEW check(increasing == gb >= ga || (equalsWithinTolerance(ga, 0.0) && equalsWithinTolerance(gb, 0.0))); 

Changed assert comparison on line 493

OLD check(g0 == 0.0 || gPositive == (g0 > 0.0));

NEW check(equalsWithinTolerance(g0, 0.0) || gPositive == (g0 > 0.0));

In general comparing a double to exactly zero is obviously bad but I wasn't sure if this was done because even if it was within machine epsilon error we'd want these conditions to be evaluated as false.  If you'd like me to make the change to EventState to accommodate this we could make the tolerance a configurable parameter with a default so that users could set it all the way to machine epsilon if they want (perhaps that's the default value) but expand it if they wanted to via something like a programmatic override.  

Thoughts?

Hank