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Eric Coissac
8c7017a99d
- Update obioptions.Version from "Release 4.4.29" to "/v/ Release v5" - Update version.txt from 4.29 → .30 (automated by Makefile)
32 lines
1.7 KiB
Markdown
32 lines
1.7 KiB
Markdown
# Semantic Description of `obitax.LCA()` Functionality
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The `LCA` method computes the **Lowest Common Ancestor (LCA)** of two taxonomic entities (`Taxon` instances) within a shared hierarchical taxonomy.
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- **Input**: A pointer to another `*Taxon` (`t2`) and the receiver taxon (`t1`).
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- **Output**: A `*Taxon` representing their LCA, or an error detailing why computation failed.
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### Core Logic
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- **Nil Safety**: Handles cases where one or both taxa are `nil`, returning the non-nil taxon (or an error if *both* are nil or lack internal `Node` references).
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- **Validation Checks**:
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- Ensures both taxa belong to the *same* `Taxonomy`.
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- Verifies that the taxonomy is **rooted** (i.e., has a defined root node).
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- **Path-Based Traversal**:
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- Retrieves the full path from each taxon to the root via `Path()` (assumed to return an ordered list of nodes).
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- Traverses both paths *backwards* (from root toward leaves) until divergence is detected.
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- The first divergent node marks the boundary; the LCA is the last *common* ancestor (i.e., `slice[i+1]` after loop exit).
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### Semantic Meaning
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- The LCA represents the most specific taxonomic node that *contains both taxa* in its subtree.
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- This operation is foundational for tasks like:
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- Taxonomic classification consistency checks,
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- Phylogenetic inference (e.g., computing taxon distances),
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- Hierarchical aggregation in biodiversity analyses.
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### Error Handling
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Explicit errors cover:
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- Invalid inputs (`nil` taxa, missing nodes),
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- Cross-taxonomy queries,
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- Unrooted taxonomy (undefined root → no unique LCA possible).
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This implementation assumes a **directed acyclic graph** (specifically, a tree) structure for the taxonomy hierarchy.
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