potential_false_negative column

[bluegenes]

Potential false negative was a mistake column for gather results, because we can never get a false negative. By definition, every gather result is a positive sequence match we obtained with prefetch.

When used correctly, potential_false_negative indicates a situation where the sketch size and /or scaling of one or both sketches means we are unlikely to find a match, regardless of sequence similarity.

We can get false negatives when doing pairwise or search without greedy gather decomposition. It would not be a mistake to include this column in manysearch results, for example, if we use the “—write-all” to write rows without matches. Same for pairwise, multisearch, compare.

Since we have traditionally just written files with only the matching results for e.g. prefetch/search, it is not currently being used.