Architecture

The purpose of this document is for people editing the SPoRC codebase (contributors, successors, future-you). The goal here is to keep the package navigable as it grows, especially as spatial model development adds more moving parts. It should be updated whenever the pipeline below changes shape (a new Setup_Mod_* stage, a new section of SPoRC_rtmb.R, a new post-fit diagnostic) — treat a stale architecture doc as a bug.

Mental model

In general, SPoRC has three phases, in this order:

Setup — a chain of R functions builds up three plain lists: data, parameters, mapping. No likelihood is evaluated yet; this phase is pure data wrangling and input validation.
Fit — data and parameters are handed to RTMB::MakeADFun wrapped around a single objective function, SPoRC_rtmb(), which is optimized with nlminb + Newton refinement.
Post-fit — the fitted object (obj$rep, obj$sdrep, obj$optim) is passed to diagnostics, reference-point, plotting, and resampling routines.

Setup_Mod_Dim()
   -> Setup_Mod_Rec()
   -> Setup_Mod_Biologicals()
   -> Setup_Mod_Movement()
   -> Setup_Mod_Tagging()
   -> Setup_Mod_Catch_and_F()
   -> Setup_Mod_SrvIdx_and_Comps()
   -> Setup_Mod_Srvsel_and_Q()
   -> Setup_Mod_Weighting()
        |
        v  input_list$data, input_list$par, input_list$map
   fit_model(data, parameters, mapping)
        |  RTMB::MakeADFun(cmb(SPoRC_rtmb, data), parameters, map = mapping)
        |  nlminb() + Newton steps
        v
   obj  (obj$rep, obj$sdrep, obj$optim)
        |
        +--> Get_Reference_Points()      (SPR / MSY / Fmsy by structure)
        +--> get_model_fits() / plot_*   (index, comp, OSA residual diagnostics)
        +--> do_retrospective(), do_jitter(), do_likelihood_profile(), run_francis()
        +--> Do_Population_Projection(), closed_loop_simulations()

The `input_list` accumulator pattern

Every Setup_Mod_* function takes an input_list (initialized by Setup_Mod_Dim() as list(data = list(), par = list(), map = list())) and returns it with more keys filled in. This is the central structure of the package: setup functions are pipeline stages that thread one growing list through each other, not independent builders. Order generally matters — later stages read dimensions (input_list$data$n_regions, etc.) set by earlier ones, and default arguments frequently reference input_list$data$... in their own definitions (see Setup_Mod_Rec()’s defaults for an example).

At the end of the chain, input_list$data, input_list$par, and input_list$map are unpacked and passed to fit_model(). Setup_Sim_* functions (in the same files as their Setup_Mod_* counterparts) follow the identical accumulator pattern but build inputs for Simulate_Population.R’s operating model instead of for fitting.

`SPoRC_rtmb()` — the objective function

R/SPoRC_rtmb.R is the one RTMB objective function for every model configuration the package supports; there is no per-model-type branching at the file level; instead the objective always runs but is regulated by the data switches set during Setup (e.g. rec_model, move_type, which likelihood/OSA flags are on). Concretely it moves through, in order: parameter transforms (movement, natural mortality, selectivity) -> mortality -> recruitment -> initial age structure -> population projection -> observation models (fishery, survey, tagging) -> likelihood components (retained/discarded catch, indices, compositions, tags) -> priors and penalties.

If you’re adding a new data source or process to the model, this is the file where its likelihood contribution gets wired in; the corresponding Setup_Mod_* function is where its data/parameters/mapping get prepared beforehand.

Naming conventions

The prefix on a function name generally tells you its role in the pipeline:

Prefix	Role
`Setup_Mod_*`	Builds `data`/`parameters`/`mapping` for a real fit, one life-history process or data source per file (`Setup_Rec.R`, `Setup_Biologicals.R`, `Setup_Movement.R`, `Setup_Fishery.R`, `Setup_Survey.R`, `Setup_Tagging.R`, `Setup_Observation_Processes.R`).
`Setup_Sim_*`	Same role, but for the operating model in `Simulate_Population.R` (self-tests, closed-loop simulation). Lives alongside its `Setup_Mod_*` counterpart in the same file.
`do_*_mapping`	Private helper (not exported) inside a `Setup_*` file that builds the RTMB `map` factor list for one parameter block — this is how parameters get fixed, shared across blocks, or turned into random-effect deviations.
`Get_*`	Pulls a derived quantity out of already-set-up data/parameters/a fitted object: `Get_Movement`, `Get_Selex`, `Get_Reference_Points`, `Get_Init_NAA`, `Get_Det_Recruitment`.
`do_*` (lowercase, top-level)	A post-fit procedure that re-runs or perturbs a fitted model: `do_retrospective`, `do_jitter`, `do_likelihood_profile`, `do_runs_test`, `do_francis`.
`get__plot` / `get__fits`	Post-fit plotting/tabulation, mostly in `Make_Plots_Tables.R` and `get_model_fits.R`.

Within SPoRC_rtmb.R the same ## Section / ### Subsection comment banner style is used consistently — keep using it there if you extend the file, since it’s the only navigation aid for a ~2,800-line function.

File map

R/
  Setup_Dimensions.R          entry point: n_regions, n_pop, ages, years, seasons...
  Setup_Rec.R                 recruitment model, steepness, rec devs, stray/season/sex-ratio pars
  Setup_Biologicals.R         growth, weight-at-age, maturity, natural mortality
  Setup_Movement.R            movement parameterization (rates, blocks, continuous PE)
  Setup_Tagging.R             conventional tagging design, reporting, shedding
  Setup_Fishery.R             catch, F, discard mortality, fishery comps setup
  Setup_Survey.R              survey indices, comps, selectivity, catchability
  Setup_Observation_Processes.R  likelihood weighting across data sources
  Setup_Containers.R          shared array/container scaffolding for Setup_Sim_*
  SPoRC_rtmb.R                the RTMB objective function (see above)
  fit_model.R                 MakeADFun + nlminb + Newton refinement wrapper
  Get_Movement.R, Get_Selex.R, Get_Det_Recruitment.R, Get_Init_NAA.R
                               derived-quantity helpers used inside SPoRC_rtmb.R
  Get_PE_loglik.R             process-error / random-effect log-likelihood + penalty helpers
  Get_Comp_Likelihoods.R, Get_Conv_Tag_Likelihoods.R
                               composition and tag-recapture likelihood assembly
  Get_Reference_Points.R      SPR/BH-MSY solvers (single-region, global, local x sgl/multi-pop)
  Get_3d_precision.R          GMRF/precision-matrix helpers for correlated deviations
  Distributions.R             custom density functions (Dirichlet, Dirichlet-multinomial,
                               negative binomial, OSA residual machinery) used by RTMB and sims
  Build_PE_Map.R              shared process-error map-building across parameter blocks
  Do_Population_Projection.R  forward projection off a fitted model
  Simulate_Population.R       operating model: simulate data forward given true dynamics
  Simulate_RV.R                random-variate generators used by the simulator
  closed_loop_simulations.R   condition + run closed-loop MSE, given an OM and estimator
  do_retrospective.R, do_jitter.R, do_likelihood_profile.R, do_runs_test.R, do_francis.R
                               post-fit diagnostics / resampling procedures
  get_model_fits.R            OSA residuals, fitted vs. observed comps/indices
  Make_Plots_Tables.R         ggplot2 plotting and summary tables
  Utility_Functions.R         cross-cutting helpers (cmb() currying, safe_extract,
                               parameter-mapping introspection, misc math)
  check_dimensions.R          input validation for data/sim dimension lists
  release_tag_attr.R          tag-release attribute bookkeeping
  data.R                      documents the bundled example datasets in data/

Test files in tests/testthat/ mirror this structure loosely by feature (test-movement.R, test-fdev_pe.R, test-getselex.R, …) plus a set of end-to-end regression tests against bundled example fits (test-mlt_rg_*, test-ebs_pol_sgl_rtmb*.R, test-dusky_rtmb.R) that pin down obj$rep/nll values for known configurations — these are the tests most likely to catch an accidental change in SPoRC_rtmb.R’s numerics.

Extending the model: a checklist

Adding a new process, fleet type, or data source touches the pipeline in a predictable set of places:

Setup: add or extend a Setup_Mod_* function to accept the new spec, validate it, and append the resulting entries to input_list$data / $par / $map. If parameters need fixing/sharing, add a do_*_mapping helper in the same file.
Objective: add a ## Section in SPoRC_rtmb.R that consumes the new data/parameters entries and contributes to jnll/nll — put it in the section it belongs to (transform, observation model, or likelihood/prior) rather than appending to the end.
Sim counterpart: if the process should be simulate-able, add the matching Setup_Sim_* inputs and generation logic in Simulate_Population.R.
Post-fit: expose derived output through Get_* (if other code needs to reuse the derived quantity) and/or Make_Plots_Tables.R / get_model_fits.R (if it needs to be seen).
Tests: add a targeted testthat test near the feature, and check whether the test-mlt_rg_* / test-*_rtmb.R regression tests need updated reference values.
Vignette: if the feature is user-facing, document it in the relevant lettered vignette (see the Articles index) rather than only in code comments.