Commits on Oct 12, 2022

1. Warn about loss of precision in FDBSCAN-DenseBox …

   For some problems and eps, FDBSCAN-DenseBox may suffer from severe loss
   of precision when computing cellBox(). This may result in wrong DBSCAN
   results.
   
   Initially, the problem was observed on a full NGSIM dataset:
   ```
   $ ./ArborX_DBSCAN.exe --binary \
       --filename /data/data_and_logs/2021_02_20_dbscan_datasets/mustafa_2019/ngsim.arborx \
       --print-dbscan-timers --core-min-size 2 --eps 1.0 --max-num-points 90000 \
       --impl fdbscan-densebox --verify
   <...>
   Core point is marked as noise: 41888 [-1]
   Core point is marked as noise: 17027 [-1]
   Core point is marked as noise: 43104 [-1]
   ```
   Tracking down the issue revealed that a point 2279 (part of a dense
   cell) was finding point 10369 (not part of a dense cell), but the
   reverse was not true (i.e., 10369 was not finding the dense cell that
   2279 was in). Studying the dense boxes, I observed that the problematic
   box had bounds
     [[6452399.000000,1872182.375000,0.000000],
      [6452399.000000,1872183.000000,0.577350]]
   Note the same x coordinate for both min and max corner. The h in this
   run was ~0.57. So it completely got lost. Even Y coordinate lost some
   precision, though not as much.

   

   aprokop committed Oct 12, 2022
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