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Changelog

Source: NEWS.md

gkwdist 1.1.1

Major Refactoring Release

This release represents a comprehensive refactoring of the entire package codebase, focusing on numerical stability, code consistency, and maintainability.

C++ Backend Overhaul

  • Unified utility functions: Introduced utils.h header providing numerically stable implementations of critical functions:

    • log1mexp(): Stable computation of log(1 - exp(x)) using Mächler (2012) methodology
    • log1pexp(): Overflow-protected computation of log(1 + exp(x))
    • safe_log(), safe_exp(), safe_pow(): Protected arithmetic operations with graceful handling of edge cases
    • Vectorized versions (vec_safe_log, vec_log1mexp, etc.) for efficient array operations

  • Consistent parameter validation: All distribution families now use dedicated parameter checkers (check_pars(), check_kw_pars(), check_ekw_pars(), etc.) that properly handle NaN, Inf, and boundary conditions.

  • Complete documentation: All C++ source files now include comprehensive Doxygen-style documentation headers describing:

    • Mathematical formulas for PDF, CDF, quantile, and random generation
    • Parameter constraints and special cases
    • Numerical stability considerations
    • Relationship to parent GKw distribution

Bug Fixes

  • Fixed critical bug in qgkw(): Corrected logic error where lower_tail transformation was incorrectly applied when log_p = TRUE. The probability is now properly converted to linear scale before tail adjustment.

  • Fixed gradient calculation in grkkw(): Resolved issue where log_z was not recomputed after clamping z to minimum threshold, causing corrupted gradient values near boundaries.

  • Fixed Hessian calculation in hsmc(): Corrected sign errors and formula for the lambda component of the Hessian matrix for the Beta-Power/McDonald distribution.

  • Fixed gradient signs in grmc(): Ensured consistent computation of log-likelihood gradient before negation for optimization.

Code Quality Improvements

  • Eliminated unused variables: Removed declared but unused constants (exp_threshold) and intermediate variables across all distribution files.

  • Removed redundant calculations: Streamlined computations, notably in pgkw() where logarithm was computed twice for the same quantity.

  • Simplified parameter recycling: Replaced double-modulo indexing pattern (idx = i % k; vec[idx % vec.n_elem]) with direct single-modulo access (vec[i % vec.n_elem]) in random generation functions.

  • Standardized function signatures: All distribution functions now follow consistent patterns for parameter order, validation, and return value handling.

R Wrapper Layer

  • Complete separation of R and C++ interfaces: All exported R functions now serve as wrappers around internal C++ implementations (.dgkw_cpp, .pgkw_cpp, etc.), providing:
    • Enhanced input validation with informative error messages
    • Consistent argument checking across all distribution families
    • Proper NA/NaN propagation
    • Documentation accessible via standard R help system

Distribution Families

All seven distribution families have been refactored with identical improvements:

Distribution Parameters File
Generalized Kumaraswamy (GKw) α, β, γ, δ, λ gkw.cpp
Kumaraswamy-Kumaraswamy (KKw) α, β, δ, λ kkw.cpp
Beta-Kumaraswamy (BKw) α, β, γ, δ bkw.cpp
Exponentiated Kumaraswamy (EKw) α, β, λ ekw.cpp
Beta-Power/McDonald (BP/Mc) γ, δ, λ bpmc.cpp
Kumaraswamy (Kw) α, β kw.cpp
Beta (GKw-style) γ, δ beta.cpp

Each family includes: density (d*), distribution (p*), quantile (q*), random generation (r*), negative log-likelihood (ll*), gradient (gr*), and Hessian (hs*) functions.

Technical Notes

  • Minimum supported R version remains 3.5.0
  • C++11 standard required (enabled via Rcpp plugin)
  • Depends on RcppArmadillo for efficient linear algebra operations

Acknowledgments

Special thanks to the thorough code review process that identified subtle numerical issues in edge cases, particularly for extreme parameter values and observations near distribution boundaries.

gkwdist 1.0.7

gkwdist 1.0.5

Documentation Improvements

  • Enhanced Examples for Likelihood Functions: All ll*, gr*, and hs* functions now include comprehensive examples demonstrating:

    • Maximum likelihood estimation with analytical gradients
    • Univariate profile likelihoods with confidence thresholds
    • 2D likelihood surfaces with confidence regions (90%, 95%, 99%)
    • Confidence ellipses with marginal intervals for parameter pairs
    • Numerical vs analytical derivative verification
    • Likelihood ratio tests and score tests

  • Professional Visualization Standards:

    • Consistent color scheme across all examples
    • Grid-adaptive algorithms for computational efficiency
    • Base R only - no external dependencies required

  • Complete Coverage: Enhanced documentation for all distribution families (Kw, EKw, KKw, GKw) covering 2 to 5 parameters

  • Theoretical References: Documentation cites foundational work by Carrasco et al. (2010), Jones (2009), Kumaraswamy (1980), and standard inference theory from Casella & Berger (2002)

gkwdist 1.0.3

  • README.md: Fix typos and faill link
    • Fix zzz.R file by removing useless texts

gkwdist 1.0.2

gkwdist 1.0.1

Major Improvements

Enhanced gkwgetstartvalues() Function

  • NEW: Added family parameter to support all distribution families
    • Automatically returns correct number of parameters for each family
    • Family-specific initial value strategies for better convergence
    • Supported families: "gkw", "bkw", "kkw", "ekw", "mc", "kw", "beta"
    • Case-insensitive family names for user convenience

Documentation Enhancements

  • README.md: Complete rewrite with mathematical rigor
    • All LaTeX formulas corrected and verified for proper rendering
    • Eight comprehensive examples using optim() with analytical gradients
    • Corrected function signatures: all ll*(), gr*(), and hs*() functions use (par, data) signature
    • Added performance benchmarks demonstrating 10-50× speedup with C++ implementation
    • Hierarchical structure diagram for all distribution families
    • Model selection workflow and practical guidelines
    • Removed all references to deprecated gkwfit() function

CRAN Submission Readiness

  • DESCRIPTION: Fixed to meet CRAN requirements
    • Proper Authors@R field formatting
    • Removed unused dependencies (numDeriv)
    • Corrected package dependencies (RcppArmadillo only in LinkingTo)
    • Enhanced description with DOI references
    • Fixed maintainer email formatting

Bug Fixes

  • Fixed function call signatures in all README examples to match actual implementation
  • Corrected parameter passing in optimization examples (now consistently use (par, data))
  • Fixed LaTeX rendering issues with \left/\right delimiters in GitHub Markdown

Testing

  • NEW: Comprehensive test suite using testthat
    • 100+ tests covering all exported functions
    • Tests for all 7 distribution families (GKw, BKw, KKw, EKw, MC, Kw, Beta)
    • PDF, CDF, quantile, and random generation tests
    • Log-likelihood, gradient, and Hessian validation
    • Parameter recovery tests with MLE
    • Edge cases and boundary condition handling
    • Integration tests for PDF-CDF consistency

Performance

  • All functions implemented in C++ for maximum computational efficiency
  • Analytical derivatives (gradient and Hessian) provide exact computations
  • Optimized numerical stability for extreme parameter values

Notes

  • This is the initial CRAN submission
  • Package focuses exclusively on distribution functions (no high-level fitting interface)
  • Companion package gkwreg provides regression modeling capabilities
  • All user-facing functions maintain backward compatibility
  • C++ implementation uses RcppArmadillo for linear algebra operations
  • Analytical functions use robust log-scale computations to prevent overflow/underflow
  • Random generation uses inverse CDF method where closed-form solutions exist

gkwdist 0.1.0

New Features

  • Initial CRAN release
  • Generalized Kumaraswamy distribution (5 parameters)
  • Six nested sub-families: Beta, Kumaraswamy, Exponentiated-Kumaraswamy, Kumaraswamy-Kumaraswamy, Beta-Kumaraswamy, and McDonald distributions
  • Complete set of distribution functions (d/p/q/r)
  • Log-likelihood, gradient, and Hessian functions for all families

Performance

  • Optimized C++ implementation via Rcpp
  • Vectorized operations for speed