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📖 Update super-kmer theory and implementation to prefer non-degenerate m-mers

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- Update super-kmer definition in `kmERS.md` to specify that non-degenerate m-mers are preferred over degenerate ones (degeneracy = homopolymer).
- Refactor `superkmer.rs`: change `.canonical()` to mutate in-place and return bool.
- Add `m` field & canonical-aware minimizer position calculation to SuperKmerIter in obiskbuilder.
- Add helper functions `is_degenerate` and minimizer comparison logic to rolling_stat.rs for consistent tie-breaking.
- Minor formatting cleanup in superkmer command and chunk processing.
This commit is contained in:
Eric Coissac
2026-04-20 17:49:52 +02:00
parent b534c693ac
commit 380b5a6f94
5 changed files with 43 additions and 22 deletions
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docmd/theory/kmers.md
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@@ -9,7 +9,7 @@ A **kmer** is a DNA subsequence of fixed length k. Two constraints govern the ch
## Super-kmers
A **super-kmer** is a maximal run of consecutive kmers from a DNA read, each overlapping the next by k−1 nucleotides. Each kmer of the run carries the same **canonical minimizer**. The **canonical minimizer** of a kmer is the smallest value of `min(m-mer, revcomp(m-mer))` over all m-mers within the kmer (m < k, m odd).
A **super-kmer** is a maximal run of consecutive kmers from a DNA read, each overlapping the next by k−1 nucleotides. Each kmer of the run carries the same **canonical minimizer**. The **canonical minimizer** of a kmer is the smallest value of `min(m-mer, revcomp(m-mer))` over all m-mers within the kmer (m < k, m odd), with the constraint that **non-degenerate m-mers are always preferred** over degenerate ones. A degenerate m-mer is one composed of a single repeated nucleotide (all-A, all-C, all-G, or all-T); such m-mers are selected only if no non-degenerate candidate exists in the window.
### Canonical super-kmers