Add logSumExp and logSumExpPair functions#84
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Implements numerically stable log-sum-exp computation (closes haskell#65). - logSumExp: vector version using the max-subtraction trick - logSumExpPair: optimized two-argument version using log1p Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Implements numerically stable log-sum-exp computation, as requested in #65.
logSumExp :: U.Vector Double -> Double— computeslog(sum(exp(x_i)))using the max-subtraction trick to avoid overflow/underflowlogSumExpPair :: Double -> Double -> Double— optimized two-argument version usinglog1pfor higher precisionThese functions are commonly used when working with log-probabilities in statistical computing and machine learning.
Changes
Numeric.SpecFunctions.Internal: implementation of both functionsNumeric.SpecFunctions: exported under a new "Log-sum-exp" sectiontests/Tests/SpecFunctions.hs: property tests (singleton, commutativity, identity) and unit tests (empty vector, large values, log-probability combination)Test plan
cabal test)-Infinity, large values (1000+) handled correctlyCloses #65