Changes in version 0.2.0 (2026-05-23)                  

New features

  - dfr_dist_series objects now also inherit from dist_structure (from
    the dist.structure package). Series-system topology generics work
    out of the box: phi, min_paths, min_cuts, system_signature, plus the
    defaults from dist.structure (structural_importance, reliability,
    dual, is_coherent, critical_states, system_lifetime,
    system_censoring, birnbaum_importance, criticality_importance,
    vesely_fussell_importance, substitute_component, compose_systems).

  - The local ncomponents and component generics are removed and
    re-exported from dist.structure instead. This eliminates a latent
    namespace collision when both serieshaz and dist.structure are
    loaded. Existing user code that calls ncomponents(sys) or
    component(sys, j) is unaffected.

Internal

  - Class chain on dfr_dist_series is now c("dfr_dist_series",
    "dfr_dist", "dist_structure", "univariate_dist", "dist"). The
    "dist_structure" insertion is positioned after "dfr_dist" so the
    optimized flexhaz survival, hazard, sampler, and CDF methods
    continue to dispatch first; "dist_structure" provides defaults only
    for generics that flexhaz/serieshaz do not already implement.

                 Changes in version 0.1.1 (2026-04-13)                  

Improvements

  - Decomposed system score and Hessian: instead of numDeriv on the full
    system log-likelihood, both are computed per-component. When
    components provide analytical score_fn/hess_fn, the cumulative
    hazard derivatives are extracted analytically (via the all-censored
    trick); the hazard derivatives use
    numDeriv::jacobian/numDeriv::hessian per-component
    (lower-dimensional). The Hessian exploits block structure:
    cross-component blocks reuse rate Jacobians from the score. Roughly
    m-fold speedup for systems with m components.

  - Input validation for component() and component_hazard(): the j
    parameter now rejects non-integer, NA, and vector inputs (previously
    j = 1.5 silently truncated to j = 1).

  - component_hazard() closure now reads the system parameter vector
    lazily, so it reflects updates to sys$par after construction (e.g.,
    after fitting).

  - Guard against zero-parameter components: the constructor now rejects
    n_par entries less than 1.

  - Aligned sys_cum_haz initialization to numeric(length(t)) for
    explicit vectorization consistency with sys_rate.

  - Added numDeriv to Imports (previously an undeclared transitive
    dependency through flexhaz).

  - Removed Remotes field from DESCRIPTION (CRAN submission blocker).

Bug Fixes

  - Fixed stale parameter capture in component_hazard() closure: default
    parameters were eagerly captured at closure-creation time, causing
    the closure to use outdated values if sys$par was updated
    post-construction.

Tests

  - Added tests for left-censored data (delta = -1), boundary conditions
    (t = 0), j parameter validation, sample_components error path, and
    decomposed score accuracy.

Known Limitations

  - Exponential series systems are not identifiable from system-level
    data alone (only the sum of rates is identifiable).

                        Changes in version 0.1.0                        

Initial release.

Features

  - dfr_dist_series() constructor composes multiple dfr_dist components
    into a series system distribution where the system hazard is the sum
    of component hazards.
  - Full inheritance from dfr_dist: hazard, survival, CDF, density,
    quantile, sampling, log-likelihood, score, Hessian, and MLE fitting
    all work automatically.
  - Analytical cumulative hazard when all components provide
    cum_haz_rate; numerical integration fallback otherwise.
  - Series-specific introspection: ncomponents(), component(),
    param_layout(), component_hazard(), sample_components().
  - Nested series system support (a dfr_dist_series can be a component
    in another series system).
  - Four vignettes: overview, mathematical foundations, MLE fitting
    workflows, and advanced composition.