# V0.3 Scope ## Summary `v0.3` is the first downstream-utility release for PDELie. It does **not** introduce a new numerical regime. It does **not** widen the ecosystem surface broadly. It does **not** bring operator methods into the stable library. Instead, it asks a narrower and more important question: > Can the current stable symmetry pipeline support one minimal invariant/downstream utility path under controlled benchmark conditions? `v0.3` is therefore the first **invariant/downstream utility** release, not the first **broad ecosystem** or **operator** release. The downstream target for `v0.3` is frozen as: - a **single-generator** invariant workflow only - a **thin downstream bridge** only - one **controlled benchmark layer** only - Heat and Burgers remain the only stable PDEs - the current stable derivative backend remains `spectral_fd` --- ## Current State ### Milestone 1 — Complete `v0.3` Milestone 1 is complete. Completed scope: - stable `InvariantMapSpec` - runtime-only `InvariantApplier` - one frozen invariant application path for the current stable symmetry slice - regression protection showing Heat and Burgers still pass the existing stable pipeline This milestone introduced the first stable invariant-layer contract without broadening the public API beyond the narrow single-generator path. ### Milestone 2 — Complete `v0.3` Milestone 2 is complete. Completed scope: - runtime-only `pdelie.discovery.to_pysindy_trajectories` - one narrow flattened-trajectory bridge for PySINDy only - one minimal downstream fit smoke path for the current invariant-transformed stable slice - no new stable canonical object This milestone added a backend-specific runtime bridge, not a canonical PDE-discovery representation. ### Milestone 3 — Complete `v0.3` Milestone 3 is complete. Completed scope: - one internal four-branch downstream benchmark: - vanilla - known_invariant - discovered_invariant - nuisance - one frozen benchmark-local alignment rule for the current single-generator translation slice - one explicit frozen PySINDy configuration for the downstream release gate - reproducibility, matched-settings, and release-gate tests - no new public API and no new stable canonical object This milestone proves a controlled downstream utility signal for the current invariant/downstream path relative to a nuisance baseline. It does not claim broader discovery-quality superiority. --- ## Must Implement ### Stable scope for `v0.3` - uniform rectilinear grids only - synthetic PDE data only - polynomial generators only - single-generator invariant workflows only - one thin downstream bridge only - one controlled benchmark layer only - verification-first development - Heat and Burgers remain supported - no new numerical backend is required for the stable path ### Stable canonical objects for `v0.3` Stable in `v0.3`: - `FieldBatch` - `DerivativeBatch` - `ResidualBatch` - `ResidualEvaluator` - `GeneratorFamily` - `VerificationReport` - `InvariantMapSpec` Runtime-only, not canonical: - `InvariantApplier` Still not stable in `v0.3`: - `InvariantLibrary` - `DiscoveryResult` No other canonical objects should become stable in `v0.3` unless absolutely necessary to support the frozen invariant/downstream path. --- ## Concrete `v0.3` Target Add one minimal end-to-end stable downstream path on top of the existing stable symmetry core. The stable conceptual path becomes: `FieldBatch -> DerivativeBatch -> ResidualBatch -> GeneratorFamily -> InvariantMapSpec -> InvariantApplier -> downstream bridge -> VerificationReport` for Heat and Burgers under the current stable translation-targeted symmetry slice. ### Required components - one stable `InvariantMapSpec` for the single-generator case - one runtime `InvariantApplier` - one thin downstream bridge, likely PySINDy - one controlled benchmark comparing: - vanilla downstream path - known-invariant downstream path - discovered-invariant downstream path - one nuisance / conditioning baseline - one release-gate layer that keeps all settings matched across benchmark branches ### Required scientific result - the known-invariant and discovered-invariant downstream paths both run end to end under the stable contracts - the benchmark is reproducible and matched - the invariant-aware downstream path is at least meaningfully distinguishable from a nuisance baseline under matched controls - Heat and Burgers remain regression-free under the existing stable symmetry pipeline `v0.3` is a utility release, not yet a broad superiority-claim release. --- ## Frozen Milestones ### Milestone 1 — Invariant layer **Status:** Complete Frozen scope: - stable `InvariantMapSpec` - runtime-only `InvariantApplier` - one narrow application path - no downstream bridge yet - no benchmark expansion yet ### Milestone 2 — Thin downstream bridge **Status:** Complete Frozen scope: - one thin downstream bridge only - no broad system-identification framework - no new canonical stable object unless absolutely required - no benchmark expansion yet beyond the minimal bridge smoke path - no weak-form methods - no operator methods - no broad adapters Completed outcome: - transformed data from the current single-generator invariant path can feed one downstream workflow cleanly under stable contracts ### Milestone 3 — Controlled downstream benchmark / release-gate layer **Status:** Complete Frozen scope: - one controlled benchmark comparing: - vanilla - known-invariant - discovered-invariant - nuisance baseline - matched feature budget - matched regularization budget - matched split policy - reproducible benchmark outputs - no broad benchmark zoo - no new public benchmark API unless clearly justified Completed outcome: - `v0.3` release gate can be stated in terms of a reproducible downstream utility benchmark, not just symmetry recovery - known_invariant and discovered_invariant are expected to be numerically equivalent in the frozen Milestone 3 slice - the nuisance baseline is the actual utility comparison branch for this release gate --- ## Development Order 1. freeze `v0.3` scope 2. implement `InvariantMapSpec` 3. implement `InvariantApplier` 4. add one thin downstream bridge 5. add the controlled downstream benchmark layer 6. add nuisance / conditioning control baseline 7. add release-gate tests and documentation --- ## Explicitly Deferred The following are **not** part of stable `v0.3` scope: - weak-form derivatives as a stable backend - multi-generator invariant charts - `InvariantLibrary` as a stable contract - `DiscoveryResult` as a stable contract - broad system-identification framework work beyond one thin bridge - broad adapters (PDEBench, The Well, etc.) as release-defining work - operator symmetry - NeuralOperator integration - nonuniform rectilinear support in stable derivative code - multiple downstream backends - broad benchmark zoo - manuscript-specific experiment logic These may be explored experimentally, but they do not define `v0.3`. --- ## Benchmark Rules for `v0.3` `v0.3` should benchmark the first stable downstream utility path, not yet claim broad downstream dominance. Required controls: - fixed train/test split conventions - fixed verification defaults - fixed noise condition where applicable - fixed feature budget - fixed regularization budget - fixed derivative backend assumptions - identical benchmark settings across: - vanilla - known-invariant - discovered-invariant - nuisance baseline Required outputs: - downstream result for vanilla path - downstream result for known-invariant path - downstream result for discovered-invariant path - downstream result for one nuisance baseline - held-out evaluation under matched settings - reproducible benchmark outputs - no regression in the existing Heat/Burgers symmetry paths The benchmark must distinguish: - correctness of the invariant/downstream mechanism - conditioning effects - a controlled downstream utility signal relative to the nuisance baseline --- ## Release Gate `v0.3` is releasable only if: - the `v0.2` Heat path still passes cleanly - the `v0.2` Burgers path still passes cleanly - the single-generator `InvariantMapSpec` and `InvariantApplier` work end to end on the frozen stable path - the thin downstream bridge works for the frozen stable task - the controlled benchmark runs reproducibly under matched settings - the nuisance baseline is included - no deferred or experimental feature is required for the stable release path - the current stable contracts remain coherent after adding the first invariant/downstream layer If these conditions are not met, `v0.3` is not complete. --- ## Non-goals `v0.3` is **not**: - the release where weak-form methods become stable - the release where PDELie becomes a broad ecosystem hub - the release where operator methods become part of the stable library - the release where full invariant machinery becomes stable - the release where downstream discovery becomes a broad multi-backend framework It is the release where PDELie proves that its current stable symmetry core can support one disciplined invariant/downstream utility path. --- ## Next Expansion After `v0.3` If `v0.3` succeeds, the next credible stable step is one of: - broader invariant machinery - broader downstream semantics - broader numerics but still **not automatically** operator methods or broad ecosystem expansion. Those decisions belong to `v0.4+`, not `v0.3`.