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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)
28 lines
1.5 KiB
Markdown
28 lines
1.5 KiB
Markdown
# `obistats` Package: Semantic Overview
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The `obistats` package provides low-level statistical and combinatorial utilities in pure Go, focusing on numerical robustness and performance.
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- **Sign Function (`mathSign`)**
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Returns the sign of a `float64`: `-1`, `0`, or `+1`. Handles NaN by returning NaN.
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- **Precomputed Factorials (`smallFact`)**
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Precomputes factorials from `0!` to `20!` (fits in 64-bit signed integer), enabling fast exact binomial coefficient computation for small `n`.
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- **Binomial Coefficient (`mathChoose`)**
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Computes $\binom{n}{k}$ efficiently:
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- For `n ≤ 20`: uses integer arithmetic (multiplication + division) for exact results.
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- For larger `n`: leverages logarithms via `mathLchoose` and exponentiates (`exp(log(Choose))`) to avoid overflow.
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- **Log-Binomial Coefficient (`mathLchoose`)**
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Computes $\log \binom{n}{k}$ via the log-gamma function:
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$$\log \binom{n}{k} = \lg(n+1) - \lg(k+1) - \lg(n-k+1)$$
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Ensures numerical stability for large `n`, avoiding overflow/underflow.
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- **Internal Helper (`lchoose`)**
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Core implementation of log-binomial using `math.Lgamma`, reused by both exact and large-scale paths.
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**Design Notes**:
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- Prioritizes correctness (e.g., NaN propagation, edge-case handling).
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- Balances speed and precision: exact integer arithmetic for small inputs; log-space computation for scalability.
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- Mirrors functionality from an internal benchmarking module, adapted here as a standalone utility.
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