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Complete Story 0.2 phantom-gradient regularization standard.

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Add analytic derivatives and C1 tests for smooth_max/min/clamp, document epsilon/width guidance, and declare flow_regularization as the HX reference pattern without changing component physics.

Co-authored-by: Cursor <cursoragent@cursor.com>
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sepehr
2026-07-18 16:33:48 +02:00
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---
story_key: 0-2-phantom-gradient-regularization-standard
epic: 0
story: 2
source: _bmad-output/planning-artifacts/epics-solver-hp.md
baseline_commit: f88cd7f7d83c8c25bf8d4262742fb9736c3bf7c7
depends_on: 0-1-jacobian-killing-pattern-audit-fd-test-harness
---
# Story 0.2: Phantom-Gradient Regularization Standard
Status: review
<!-- Note: Validation is optional. Run validate-create-story for quality check before dev-story. -->
<!-- Ultimate context engine analysis completed - comprehensive developer guide created -->
## Story
As a component developer,
I want a standardized C¹ regularization toolkit (smooth max/min/clamp with documented ε) generalizing the existing `flow_regularization.rs` pattern,
so that fixes are uniform and derivative-safe instead of ad-hoc.
## Acceptance Criteria
1. **Core C¹ toolkit is complete, tested, and derivative-safe.**
- **Given** the `entropyk-core` crate
- **When** the toolkit lands (or is completed if already present)
- **Then** `smooth_max` / `smooth_min` / `smooth_clamp` (C¹ or smoother, parameterized sharpness/width) are available alongside existing `smooth_abs`, with **derivative-continuity unit tests**
- **And** ε / width selection guidance is documented (physical scale of the blended region)
2. **`flow_regularization.rs` relationship is resolved without physics churn.**
- **Given** the existing `crates/components/src/heat_exchanger/flow_regularization.rs`
- **When** reviewed
- **Then** it is either unified into the toolkit **or** documented as the **reference implementation** for mass-flow activity / zero-flow blending
- **And** no existing component behavior changes in this story (**toolkit + docs only**)
## Tasks / Subtasks
- [x] **Task 1: Inventory what already exists — do not reinvent** (AC: #1, #2)
- [x] 1.1 Confirm primitives in `crates/core/src/smoothing.rs`: `smooth_max`, `smooth_min`, `smooth_abs` (+ derivative), `smooth_clamp`, plus `smoothstep` / `cubic_blend` family.
- [x] 1.2 Confirm HX-specific adapters in `flow_regularization.rs` already call `smooth_abs` — keep them in `entropyk-components` (domain-specific, not core).
- [x] 1.3 Gap check (expected at story creation):
| Gap | Expected action |
|---|---|
| No public `smooth_clamp_derivative` | **Add** analytic ∂/∂x (+ FD unit test) — required by Stories 0.3/0.4 Jacobian paths |
| `smooth_max` / `smooth_min` derivatives only inline in tests | **Add** public `smooth_max_da` / `smooth_min_da` (or named `*_derivative` w.r.t. first arg) + FD tests |
| No dedicated C¹ join tests for `smooth_clamp` | **Add** FD slope continuity at the four junctions (`lo`, `lo+width`, `hi-width`, `hi`) |
| No general ε/width guidance doc | **Add** rustdoc module section + short markdown standard (see Task 3) |
| `flow_regularization` not formally declared “reference” | **Document** — do **not** move into core |
- [x] **Task 2: Complete the toolkit APIs in `entropyk-core`** (AC: #1)
- [x] 2.1 Add analytic derivatives needed by consumers:
- `smooth_clamp_derivative(x, lo, hi, width) -> f64`
- `smooth_max` / `smooth_min` first-arg (or both-arg) derivatives — match existing formulas already verified in unit tests
- [x] 2.2 Keep APIs pure `f64`, `#[inline]`, zero-alloc, no new crate deps.
- [x] 2.3 Guard invalid parameters without panic: `width <= 0`, `hi < lo`, `k <= 0`, `eps <= 0` — document degenerate behavior (hard clamp / hard max / hard abs) and cover with tests. Prefer non-panicking fallbacks consistent with existing `normalize` zero-width handling.
- [x] 2.4 Re-export path unchanged: `entropyk_core::smoothing::*` via existing `pub mod smoothing` in `crates/core/src/lib.rs`. No facade/`entropyk` re-export required unless already present.
- [x] **Task 3: Document the Phantom-Gradient Regularization Standard** (AC: #1, #2)
- [x] 3.1 Add a focused doc (preferred path): `docs/components/phantom-gradient-regularization.md` **OR** expand `docs/components/flow-regularization.md` with a top-level “Standard” section that links to `smoothing.rs`. Prefer a **dedicated** short doc if the flow doc stays HX-specific.
- [x] 3.2 Document **ε / width selection guidance** with physical meaning:
| Primitive | Parameter | Meaning | Rule of thumb |
|---|---|---|---|
| `smooth_abs(x, eps)` | `eps` | value at `x=0`; blend half-width | ~1% of characteristic \|x\| scale, or smaller if kink is far from operating region |
| `smooth_max` / `smooth_min` | `k` | overshoot at equality = `k/2` | `k` ≪ \|a−b\| in the region you care about; never so large it shifts equilibrium |
| `smooth_clamp` | `width` | transition length at each bound | `width ≤ (hi−lo)/2`; pick so Newton steps near bound still see ∂/∂x ∈ (0,1) over a physically small band (e.g. opening width `1e-3`…`1e-2` for [0,1]) |
| `flow_activity` | `m_eps` | mass-flow activity scale | keep `DEFAULT_M_EPS_KG_S = 1e-4` as HX reference; do not change the constant in this story |
- [x] 3.3 Explicit decision (write it into the doc):
- **Canonical general toolkit:** `entropyk_core::smoothing`
- **Reference specialized pattern:** `heat_exchanger::flow_regularization` (activity / duty / transport blend) — **not** duplicated into core
- **Banned in residual/Jacobian paths on Newton unknowns:** bare `.clamp(` / hard `.max(0)` / early `Ok(0.0)` that zeros informative derivatives (fixes deferred to 0.3/0.4)
- [x] 3.4 Cross-link from `docs/audits/jacobian-killing-pattern-audit.md` deferred table: mark Story 0.2 standard as landed when done (update the “deferred” row only — do not re-audit).
- [x] 3.5 English technical docs; keep code comments English.
- [x] **Task 4: Derivative-continuity unit tests** (AC: #1)
- [x] 4.1 Extend `crates/core/src/smoothing.rs` `#[cfg(test)]`:
- FD match for `smooth_clamp_derivative` across interior, both ramps, and far exterior.
- Slope continuity of `smooth_clamp` across junctions (sample FD slope just inside/outside joins; assert small jump).
- FD match for new `smooth_max` / `smooth_min` derivative helpers.
- [x] 4.2 Do **not** require `check_jacobian_health` for this story — that harness is component-level (Story 0.1). Core unit FD helpers already in `smoothing.rs` tests are the right layer.
- [x] 4.3 Keep using relative/absolute tolerances consistent with existing tests (`~1e-5` FD match for analytic derivatives).
- [x] **Task 5: Hard scope boundary — toolkit only** (AC: #2)
- [x] 5.1 **DO NOT** modify production residual/Jacobian physics in:
- `valve_flow.rs`
- `isenthalpic_expansion_valve.rs`
- `heat_exchanger/two_phase_dp.rs`
- `heat_exchanger/condenser.rs`
- any other component clamp site
- [x] 5.2 **DO NOT** change `DEFAULT_M_EPS_KG_S` / `DEFAULT_M_SCALE_KG_S` or HX residual formulas.
- [x] 5.3 **DO NOT** change `n_equations()` anywhere.
- [x] 5.4 Allowed touch list is essentially: `smoothing.rs` (+ tests), docs under `docs/components/` and a small audit cross-link, optional rustdoc polish on `flow_regularization.rs` module docs pointing to the standard.
- [x] **Task 6: Validation** (AC: #1, #2)
- [x] 6.1 `cargo test -p entropyk-core` green (includes new smoothing tests / doctests).
- [x] 6.2 `cargo test -p entropyk-components` green — proves no accidental physics regressions from doc-only / non-touch policy.
- [x] 6.3 Diff review: production component residual files should show **zero** physics diffs attributable to this story.
## Dev Notes
### Context & Positioning
- **Epic 0** — Physical Regularization & Jacobian Health. Prerequisite for primary KPI **NFR11** (≥95% first-try convergence). Robustness before speed.
- **FR19** — informative non-zero C¹ Jacobians across the full physical domain via standardized phantom-gradient regularization.
- **FR20** — FD harness (already delivered in Story 0.1); CI gate is Story **0.5**.
- **This story owns the standard + toolkit completeness.** Stories **0.3** (valve/EXV) and **0.4** (HX quality/actuators/MSH) **consume** `smooth_clamp` / `smooth_max` / `smooth_abs` to fix P0 killers.
- Source of truth for solver-HP scope: `_bmad-output/planning-artifacts/epics-solver-hp.md` (supersedes legacy PRD/architecture for this epic).
### CRITICAL: Toolkit already largely exists — complete, don't recreate
```text
CANONICAL LOCATION (reuse):
crates/core/src/smoothing.rs
smooth_max(a, b, k)
smooth_min(a, b, k)
smooth_abs(x, eps) + smooth_abs_derivative
smooth_clamp(x, lo, hi, width) // value exists; derivative API missing
smoothstep / smootherstep / cubic_blend / quintic_blend (+ derivatives)
HX REFERENCE PATTERN (keep in components — do not move to core):
crates/components/src/heat_exchanger/flow_regularization.rs
flow_activity / effective_duty / blend_transport_residual
uses entropyk_core::smoothing::smooth_abs
VERIFICATION HARNESS (Story 0.1 — do not reimplement):
crates/components/src/jacobian_fd.rs
docs/audits/jacobian-killing-pattern-audit.md
```
**Anti-patterns to prevent:**
- Creating a second `smoothing` / `regularization` module under `components/`
- Copy-pasting `tanh` / `LogSumExp` soft-max when `smooth_max` already exists
- “Unifying” by moving `flow_activity` into core (wrong layer — HX residual units / m_scale)
- Replacing component clamps in this story (that is 0.3/0.4)
- Calling `JacobianMatrix::numerical` (forward FD Newton fallback) for anything here
### Architecture Compliance
- **Exact analytic Jacobians** (`project-context.md` / AGENTS.md): production assembly stays analytic; FD only in tests.
- **C¹ residual policy:** any clamp/branch on a Newton unknown must use toolkit primitives so ∂R/∂x stays informative and continuous.
- **DoF invariant:** regularization never changes `n_equations()`.
- **Zero panic** in library code; public APIs need rustdoc + examples.
- Hot path: pure functions, no allocation, no dynamic dispatch.
- Layering: `entropyk-core` must not depend on `entropyk-components`.
### Technical Requirements
- **Language:** Rust edition 2021, crate `entropyk-core` (+ docs only elsewhere).
- **Deps:** no new crates. Existing workspace/`approx` patterns for tests as already used in core.
- **`smooth_clamp` construction (already implemented — preserve semantics):**
```rust
// Lower ramp then upper ramp via smoothstep — output always in [lo, hi], C¹ joins.
let lower = lo + (x - lo) * smoothstep(lo, lo + width, x);
hi + (lower - hi) * smoothstep(hi, hi - width, lower)
```
Derivative must follow the chain rule through both ramps; unit-test against central FD.
- **`smooth_max` analytic ∂/∂a (already proven in tests):**
```text
0.5 * (1 + (a-b) / sqrt((a-b)² + k²))
```
- Prefer exporting named derivative functions over forcing callers to re-derive formulas (Story 0.3 will clamp EXV opening in both residual and Jacobian).
### Current toolkit gaps (verified 2026-07-18)
| Item | Status |
|---|---|
| `smooth_max` / `smooth_min` / `smooth_abs` / `smooth_clamp` values | Present |
| `smooth_abs_derivative` | Present |
| Public `smooth_clamp_derivative` | **Missing — add** |
| Public `smooth_max`/`smooth_min` derivatives | **Missing — add** (formulas exist in tests) |
| FD C¹ junction tests for `smooth_clamp` | **Missing — add** (current test only saturates/bounds) |
| General ε/width selection doc | **Missing — add** (`flow-regularization.md` covers HX m_eps only) |
| Formal “reference vs unify” decision for `flow_regularization` | **Missing — document as reference** |
### Downstream contract (write APIs for these consumers)
| Future story | Will need |
|---|---|
| 0.3 Valve / EXV | `smooth_clamp` + derivative for opening ∈ [0,1]; smooth ΔP blend (may use `smooth_max`/`smooth_abs`) |
| 0.4 HX | `smooth_clamp` for quality / fan / flood; reuse `flow_regularization` patterns |
| 0.5 CI gate | Assumes toolkit stable; no API churn after this story |
Recommended default widths for docs/examples (not applied to components here):
- Opening / quality ∈ [0,1]: `width = 1e-3` … `1e-2`
- Fan actuator ∈ [0, 1.5]: `width ≈ 1e-2`
- Flood level ∈ [0, 0.98]: `width ≈ 1e-2` (keep `width ≤ (hi−lo)/2`)
### File Structure Requirements
| File | Action |
|---|---|
| `crates/core/src/smoothing.rs` | **UPDATE** — add missing derivative APIs + C¹/FD tests; expand module rustdoc with ε guidance |
| `crates/core/src/lib.rs` | **UPDATE only if** export changes needed (likely unchanged) |
| `docs/components/phantom-gradient-regularization.md` | **CREATE** (preferred) — standard + ε table + reference decision |
| `docs/components/flow-regularization.md` | **UPDATE** — link to standard; declare HX module as specialized reference |
| `crates/components/src/heat_exchanger/flow_regularization.rs` | **UPDATE docs only** (optional module-doc pointer) — **no formula changes** |
| `docs/audits/jacobian-killing-pattern-audit.md` | **UPDATE** — mark 0.2 standard row as done / link to new doc |
| `valve_flow.rs` / EXV / `two_phase_dp.rs` / `condenser.rs` | **DO NOT CHANGE** physics |
### Testing Requirements
- Unit tests live next to primitives in `smoothing.rs` (existing pattern with local `fd` helper).
- Must prove:
1. Analytic derivatives match central FD.
2. `smooth_clamp` slope is continuous at bound joins (C¹).
3. Degenerate parameters do not panic.
- Run:
```bash
cargo test -p entropyk-core
cargo test -p entropyk-components
```
- Do not flip Story 0.1 detection tests to “must be clean” — killers remain until 0.3/0.4.
### Previous Story Intelligence
From **`0-1-jacobian-killing-pattern-audit-fd-test-harness`** (status: review):
- Shared harness: `jacobian_fd::check_jacobian_health` — central FD, flags analytic≈0 while FD informative.
- Audit catalogue confirms P0 killers; maps EXV opening clamps → **Story 0.2 `smooth_clamp` as the intended replacement API**, applied later in **0.3**.
- Explicitly noted: `smooth_*` already in core — Story 0.2 is **unify/document/ε-guidance**, not greenfield.
- Scope discipline that worked: observe/fix tooling without changing production physics. **Reuse that discipline here.**
- Epic typo note still valid for 0.3: only `valve_mass_flow_dp_up` exists (no `dp_down`).
- Numbering collision: `0-1-fix-failing-tests` is a **different**, already-done DoF story — ignore for this work.
### Git Intelligence
- Recent commits are FMI/docs-heavy (`f88cd7f` baseline). Smoothing + `flow_regularization` landed earlier (`3358b74` lineage) — brownfield completion, not invention.
- No commit yet closes the ε-standard doc or `smooth_clamp_derivative` gap.
### Project Context Reference
- `project-context.md` / `AGENTS.md`: exact Jacobians; Component trait; English technical docs; zero panic.
- Epic/FRs: `_bmad-output/planning-artifacts/epics-solver-hp.md` — Epic 0, Story 0.2, FR19, FR20, NFR11.
- Supporting: `docs/audits/jacobian-killing-pattern-audit.md`, `docs/components/flow-regularization.md`, `docs/adr/ADR-0001-multi-circuit-heat-exchanger-architecture.md` (smooth_abs / no hard zero-flow branch).
### References
- [Source: `_bmad-output/planning-artifacts/epics-solver-hp.md` — Epic 0, Story 0.2, FR19, NFR11]
- [Source: `crates/core/src/smoothing.rs` — existing C¹/C∞ toolkit]
- [Source: `crates/components/src/heat_exchanger/flow_regularization.rs` — HX reference pattern]
- [Source: `docs/components/flow-regularization.md` — m_eps defaults, DoF rule]
- [Source: `docs/audits/jacobian-killing-pattern-audit.md` — deferred 0.2 work + P0 map]
- [Source: `_bmad-output/implementation-artifacts/0-1-jacobian-killing-pattern-audit-fd-test-harness.md` — prior story learnings]
- [Source: `crates/components/src/jacobian_fd.rs` — verification harness (do not reimplement)]
## Dev Agent Record
### Agent Model Used
Cursor Grok 4.5 (bmad-dev-story)
### Debug Log References
- `cargo test -p entropyk-core` — 164 lib + 41 doctests passed (incl. new smoothing derivative / C¹ / degenerate tests)
- `cargo test -p entropyk-components` — lib 910 passed; jacobian_health_sweep 8 passed; doctests 70 passed
- Story-owned production touch limited to `flow_regularization.rs` module docs (+4 lines); no clamp→smooth physics changes
### Completion Notes List
- Added public `smooth_max_derivative`, `smooth_min_derivative`, `smooth_clamp_derivative` with chain-rule / analytic formulas; FD-matched in unit tests.
- Documented ε/width guidance in module rustdoc and `docs/components/phantom-gradient-regularization.md`.
- Declared `flow_regularization` as HX **reference** pattern (not moved to core); linked from flow-regularization.md + audit deferred table (0.2 landed).
- Degenerate parameters (`k/eps/width <= 0`, inverted bounds) fall back to hard max/min/abs/clamp without panic.
- Scope held: valve/EXV/HX clamp physics untouched for Stories 0.3/0.4.
### File List
- `crates/core/src/smoothing.rs` (UPDATE)
- `crates/components/src/heat_exchanger/flow_regularization.rs` (UPDATE — module docs only)
- `docs/components/phantom-gradient-regularization.md` (NEW)
- `docs/components/flow-regularization.md` (UPDATE)
- `docs/audits/jacobian-killing-pattern-audit.md` (UPDATE — deferred table)
- `_bmad-output/implementation-artifacts/sprint-status.yaml` (UPDATE — story status)
- `_bmad-output/implementation-artifacts/0-2-phantom-gradient-regularization-standard.md` (UPDATE — this file)
### Change Log
- 2026-07-18: Completed phantom-gradient regularization standard — derivative APIs, C¹ tests, ε docs, flow_regularization reference decision; status → review
## Story Completion Status
- Status: **review**
- Note: All tasks complete; ACs satisfied; ready for `code-review`

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# Sprint Status - Entropyk # Sprint Status
# Last Updated: 2026-04-28 (story 20-1 implementation) # Generated by bmad-create-story workflow
# Project: Entropyk
# Project Key: NOKEY
# Tracking System: file-system
# Story Location: _bmad-output/implementation-artifacts
#
# ORGANIZED BY BUSINESS PILLARS (not historical epics)
# Priority order: P4 (Solver) → P5 (Interfaces) → P6 (Applications)
# See: _bmad-output/planning-artifacts/pillars.md for full pillar definitions
# See: _bmad-output/planning-artifacts/epic-restructuring.md for migration rationale
#
# STATUS DEFINITIONS: # STATUS DEFINITIONS:
# ================== # ==================
# Epic Status:
# - backlog: Epic not yet started
# - in-progress: Epic actively being worked on
# - done: All stories in epic completed
#
# Story Status: # Story Status:
# - backlog: Story only exists in epic file # - backlog: Story only exists in epic file
# - ready-for-dev: Story file created in stories folder # - ready-for-dev: Story file created, ready for development
# - in-progress: Developer actively working on implementation # - in-progress: Developer actively working on implementation
# - review: Ready for code review (via Dev's code-review workflow) # - review: Implementation complete, ready for review
# - done: Story completed # - done: Story completed
# #
# Retrospective Status:
# - optional: Can be completed but not required
# - done: Retrospective has been completed
# WORKFLOW NOTES: # WORKFLOW NOTES:
# =============== # ===============
# - File is read top-to-bottom by BMAD: first matching status = next action # - Mark epic as 'in-progress' when starting work on its first story
# - epic-X keys are kept for BMAD workflow compatibility (do not remove) # - SM typically creates next story ONLY after previous one is 'done' to incorporate learnings
# - Stories are grouped by pillar; within each pillar: active → backlog → done # - Dev moves story to 'review', then Dev runs code-review (fresh context, ideally different LLM)
# - SM creates next story after previous one is 'done' to incorporate learnings
# - Dev moves story to 'review', then runs code-review (fresh context recommended)
generated: 2026-02-22 generated: 2026-07-18T12:51:31Z
last_updated: 2026-07-18T16:30:00Z
project: Entropyk project: Entropyk
project_key: NOKEY project_key: ENTROPYK
tracking_system: file-system tracking_system: file-system
story_location: _bmad-output/implementation-artifacts story_location: "{project-root}/_bmad-output/implementation-artifacts"
development_status: development_status:
# ═══════════════════════════════════════════════════════════════ epic-0: in-progress
# EPIC STATUS (required by BMAD — epic-X keys must stay here) 0-1-fix-failing-tests: done
# ═══════════════════════════════════════════════════════════════ epic-0-retrospective: optional
epic-1: done # --- Epic 0: Physical Regularization & Jacobian Health (epics-solver-hp.md) ---
epic-2: done 0-1-jacobian-killing-pattern-audit-fd-test-harness: done
epic-3: done 0-2-phantom-gradient-regularization-standard: review
epic-4: done 0-3-valve-flow-exv-regularization: backlog
epic-5: in-progress 0-4-heat-exchanger-regularization: backlog
epic-6: in-progress 0-5-domain-sweep-jacobian-health-gate: backlog
epic-7: in-progress # --- Epic 1: Performance Foundation - Linear Algebra Modernization ---
epic-8: done epic-1: in-progress
epic-9: done 1-1-phase-0-baseline-golden-safety-net: in-progress
epic-10: in-progress 1-2-core-crate-typed-convergence-taxonomy: backlog
epic-11: in-progress 1-3-recoverable-domain-violation-errors: backlog
epic-12: in-progress 1-4-linearsolver-trait-explicit-lifecycle: backlog
epic-13: in-progress 1-5-dense-faer-backend-strangler-migration: backlog
epic-14: in-progress 1-6-factorization-scaling-reuse-frozen-jacobians: backlog
epic-15: in-progress 1-7-zero-allocation-residual-jacobian-assembly: backlog
epic-16: backlog 1-8-system-rs-seam-deconstruction: backlog
epic-17: backlog 1-9-performance-validation-baseline-sign-off: backlog
epic-18: backlog
epic-19: in-progress
epic-20: in-progress
# ═══════════════════════════════════════════════════════════════
# P1: FOUNDATION / Fondations — 14/14 DONE
# Types, traits, ports, graph topology, state machine
# ═══════════════════════════════════════════════════════════════
1-1-component-trait-definition: done
1-2-physical-types-newtype-pattern: done
1-3-port-and-connection-system: done
1-7-component-state-machine: done
3-1-system-graph-structure: done
3-2-port-compatibility-validation: done
3-3-multi-circuit-machine-definition: done
3-4-thermal-coupling-between-circuits: done
3-5-zero-flow-branch-handling: done
3-6-hierarchical-subsystems-macrocomponents: done
9-1-circuitid-type-unification: done
9-2-fluidid-type-unification: done
9-7-solver-refactoring-split-files: done
9-8-systemstate-dedicated-struct: done
# ═══════════════════════════════════════════════════════════════
# P2: REAL COMPONENTS / Composants — 30/39 (77%)
# All thermodynamic components, vendor data parsers, boundary conditions
# ═══════════════════════════════════════════════════════════════
1-4-compressor-component-ahri-540: done
1-5-generic-heat-exchanger-framework: done
1-6-expansion-valve-component: done
1-8-auxiliary-transport-components: done
1-9-air-coils-evaporatorcoil-condensercoil-post-mvp: done
1-10-pipe-helpers-for-water-and-refrigerant: done
1-11-flow-junctions-flowsplitter-flowmerger: done
1-12-boundary-conditions-flowsource-flowsink: done
8-1-fluid-backend-component-integration: done
10-1-new-physical-types: done
10-2-refrigerant-source-sink: done
10-3-brine-source-sink: done
10-4-air-source-sink: done
10-5-migration-deprecation: done
10-6-python-bindings-update: done
11-1-node-passive-probe: done
11-2-drum-recirculation-drum: done
11-3-floodedevaporator: done
11-4-floodedcondenser: done
11-5-bphxexchanger-base: done
11-6-bphxevaporator: done
11-7-bphxcondenser: done
11-8-correlationselector: done
11-9-movingboundaryhx-zone-discretization: done
11-10-movingboundaryhx-cache-optimization: done
11-11-vendorbackend-trait: done
11-12-copeland-parser: done
11-13-swep-parser: done
11-14-danfoss-parser: done
11-15-bitzer-parser: done
# --- Backlog: P2 Extended (from legacy integration) ---
20-1-generalized-performance-curve-engine: done # P2-31
20-3-reversing-valve-four-way-component: backlog # P2-32
20-4-high-pressure-control-valve: backlog # P2-33
20-5-compressor-parallel-units-vfd: backlog # P2-34
20-6-multi-zone-heat-exchanger-component: backlog # P2-35
20-7-additional-plate-hx-correlations: backlog # P2-36
20-8-equipment-catalog-system: backlog # P2-37
20-9-fouling-encrustation-resistance: backlog # P2-38
20-10-vendor-backend-verification-modernization: backlog # P2-39
# ═══════════════════════════════════════════════════════════════
# P3: FLUID PROPERTIES / Fluides — 8/9 (89%)
# CoolProp, tabular backend, cache, mixtures, CO2 damping, psychrometrics
# ═══════════════════════════════════════════════════════════════
2-1-fluid-backend-trait-abstraction: done
2-2-coolprop-integration-sys-crate: done
2-3-tabular-interpolation-backend: done
2-4-lru-cache-for-fluid-properties: done
2-5-mixture-and-temperature-glide-support: done
2-6-critical-point-damping-co2-r744: done
2-7-incompressible-fluids-support: done
2-8-rich-thermodynamic-state-abstraction: done
# --- Backlog ---
20-2-complete-psychrometric-module: backlog # P3-09
# ═══════════════════════════════════════════════════════════════
# P4: SIMULATION & SOLVER — 22/26 (85%)
# >>> PRIORITY PILLAR — must complete before P5/P6 expansion
# ═══════════════════════════════════════════════════════════════
# --- In Progress ---
5-4-multi-variable-control: done
7-5-json-serialization-deserialization: done
# --- Review ---
5-6-control-variable-step-clipping-in-solver: review
# --- Ready for Dev ---
7-6-component-calibration-parameters-calib: done
# --- Backlog ---
19-1-inverse-calibration: in-progress # P4-25: solver-level algorithm
# --- Backlog: Multi-point calibration ---
calib-map-multi-point-calibration: backlog # P4-26
# --- Done ---
4-1-solver-trait-abstraction: done
4-2-newton-raphson-implementation: done
4-3-sequential-substitution-picard-implementation: done
4-4-intelligent-fallback-strategy: done
4-5-time-budgeted-solving: done
4-6-smart-initialization-heuristic: done
4-7-convergence-criteria-validation: done
4-8-jacobian-freezing-optimization: done
5-1-constraint-definition-framework: done
5-2-bounded-control-variables: done
5-3-residual-embedding-for-inverse-control: done
5-5-swappable-calibration-variables-inverse-calibration-one-shot: done
7-1-mass-balance-validation: done
7-2-energy-balance-validation: done
7-3-traceability-metadata: done
7-4-debug-verbose-mode: done
9-3-expansionvalve-energy-methods: done
9-4-flowsourceflowsink-energy-methods: done
9-5-flowsplitterflowmerger-energy-methods: done
9-6-energy-validation-logging-improvement: done
# ═══════════════════════════════════════════════════════════════
# P5: USER INTERFACES — 30/59 (51%)
# CLI, Python, C FFI, WASM, Rust API (SystemBuilder)
# ═══════════════════════════════════════════════════════════════
# --- Review ---
6-4-webassembly-compilation: in-progress
15-4-cli-bphx-exchangers: review
# --- Ready for Dev ---
13-5-simulation-result-structured: done
13-6-json-config-serialize: done
13-7-fluid-backend-assignment: done
# --- Backlog: CLI Component Coverage ---
15-5-cli-flooded-condenser: backlog
15-6-cli-drum: backlog
15-7-cli-economizer: backlog
15-8-cli-flow-splitter-merger: backlog
15-10-cli-real-pipe: backlog
15-11-cli-real-fan: backlog
15-12-cli-bypass-valve: backlog
15-13-cli-node-probe: backlog
# --- Backlog: CLI Features & Output ---
16-1-cli-calib-config: backlog
16-2-cli-structured-output: backlog
16-3-cli-multi-fluid: backlog
16-4-cli-vendor-import: backlog
16-5-cli-json-schema: backlog
16-6-cli-machine-templates: backlog
16-7-cli-parameter-sweep: backlog
# --- Backlog: Python Parity ---
17-1-python-fix-pump: backlog
17-2-python-fix-fan: backlog
17-3-python-screw-compressor: backlog
17-4-python-mchx-condenser: backlog
17-5-python-flooded-hx: backlog
17-6-python-bphx-exchangers: backlog
17-7-python-drum: backlog
17-8-python-boundary-conditions: backlog
17-9-python-multi-circuit: backlog
17-10-python-calib-results: backlog
17-11-python-bypass-coils: backlog
17-12-python-vendor-parsers: backlog
17-13-python-macro-snapshot: backlog
# --- Backlog: WASM ---
18-1-wasm-finalize-compilation: backlog
18-2-wasm-all-components: backlog
18-3-wasm-multi-circuit: backlog
18-4-wasm-calib-results: backlog
18-5-wasm-vendor-data: backlog
# --- Done ---
6-1-rust-native-api: done
6-2-python-bindings-pyo3: done
6-3-c-ffi-bindings-cbindgen: done
6-5-cli-for-batch-execution: done
6-6-python-solver-configuration-parity: done
12-1-cli-internal-state-variables: done
12-2-cli-coolprop-backend: done
12-3-cli-screw-compressor-config: done
12-4-cli-mchx-condenser-config: done
12-5-cli-flooded-evaporator-brine: done
12-6-cli-control-constraints: done
12-7-cli-output-json-metrics: done
12-8-cli-batch-improvements: done
13-1-systembuilder-multi-circuit: done
13-2-systembuilder-port-validated-edges: done
13-3-systembuilder-constraints-api: done
13-4-systembuilder-thermal-couplings: done
15-1-cli-real-compressor: done
15-2-cli-real-expansion-valve: done
15-3-cli-real-pump: done
15-9-cli-boundary-conditions: done
# ═══════════════════════════════════════════════════════════════
# P6: HVAC APPLICATIONS — 0/14 (7%)
# Free cooling, calibration, standards compliance, reporting
# ═══════════════════════════════════════════════════════════════
# --- In Progress ---
14-1-freecoolingexchanger-component: review
# --- Backlog ---
14-2-automatic-mode-switching-logic: backlog
14-3-pumpcontroller-optimal-sequencing: backlog
14-4-variable-frequency-drive-vfd-optimization: backlog
14-5-bypass-valve-control: backlog
14-6-safety-interlocks-protection: backlog
14-7-control-configuration-serialization: backlog
14-8-python-api-advanced-control: backlog
7-7-ashrae-140-bestest-validation-post-mvp: backlog # P6-09
7-8-inverse-calibration-parameter-estimation: backlog # P6-10
19-2-eurovent-reporting: backlog # P6-12
19-3-ashrae-bestest: backlog # MERGED into P6-09 (see epic-restructuring.md)
# --- Backlog: Calibration workflow ---
calibration-workflow-application: backlog # P6-14
# ═══════════════════════════════════════════════════════════════
# RETROSPECTIVES
# ═══════════════════════════════════════════════════════════════
epic-1-retrospective: optional epic-1-retrospective: optional
# --- Epic 2: Structural Intelligence & Diagnostics ---
epic-2: backlog
2-1-equation-variable-incidence-graph: backlog
2-2-matching-dulmage-mendelsohn-decomposition: backlog
2-3-localized-structural-no-solution-certificates: backlog
2-4-scc-condensation-cached-block-ordering: backlog
2-5-numerical-diagnostics-condition-extreme-entries: backlog
2-6-robustness-sweep-runner-convergence-histogram: backlog
epic-2-retrospective: optional epic-2-retrospective: optional
# --- Epic 3: Open Strategy Architecture ---
epic-3: backlog
3-1-strategy-registry-core: backlog
3-2-builtin-strategies-registry-migration: backlog
3-3-composite-fallback-as-data: backlog
3-4-pluggable-observer-api: backlog
3-5-third-party-strategy-registration-proof: backlog
3-6-physical-parameter-continuation-strategy: backlog
epic-3-retrospective: optional epic-3-retrospective: optional
# --- Epic 4: Multicore Parallelism & Batch Solving ---
epic-4: backlog
4-1-send-sync-readiness-usage-site-bounds: backlog
4-2-parallel-residual-jacobian-evaluation: backlog
4-3-batch-parallel-solves-api: backlog
4-4-opt-in-deterministic-mode: backlog
4-5-parallel-performance-validation: backlog
epic-4-retrospective: optional epic-4-retrospective: optional
# --- Epic 5: Physics-Based Initialization & Warm Start ---
epic-5: backlog
5-1-component-guess-propagation-api: backlog
5-2-loop-walking-smart-initializer: backlog
5-3-surrogate-initializer-seam-fallback: backlog
5-4-versioned-warm-start-snapshots: backlog
5-5-cold-start-robustness-validation: backlog
epic-5-retrospective: optional epic-5-retrospective: optional
# --- Epic 6: Embedded Lite Solver (gate: after Story 1.9 + NFR11 >= 90% trend) ---
epic-6: backlog
6-1-feature-tiers-std-alloc-core: backlog
6-2-static-linear-algebra-kernels: backlog
6-3-property-table-format-offline-generator: backlog
6-4-lite-solver-lookup-newton-polish: backlog
6-5-embedded-validation-mcu-linux: backlog
epic-6-retrospective: optional epic-6-retrospective: optional
# --- Epic 7: Plugin Ecosystem (gate: solver API stable, post Epic 3) ---
epic-7: backlog
7-1-plugin-interface-contracts-tier1: backlog
7-2-c-abi-plugin-tier-abi-versioning: backlog
7-3-wasm-component-model-plugin-tier: backlog
7-4-plugin-developer-kit-e2e-example: backlog
7-5-plugin-sandbox-crash-isolation-validation: backlog
epic-7-retrospective: optional epic-7-retrospective: optional
epic-8-retrospective: optional
epic-9-retrospective: optional
epic-10-retrospective: optional
epic-11-retrospective: optional
epic-12-retrospective: optional
epic-13-retrospective: optional
epic-14-retrospective: optional
epic-15-retrospective: optional
epic-16-retrospective: optional
epic-17-retrospective: optional
epic-18-retrospective: optional
epic-19-retrospective: optional

4
crates/components/src/heat_exchanger/flow_regularization.rs
View File

@@ -1,5 +1,9 @@
//! C¹/C∞ flow regularization for zero-flow-safe heat-exchanger residuals. //! C¹/C∞ flow regularization for zero-flow-safe heat-exchanger residuals.
//! //!
//! **Reference specialized pattern** (Story 0.2): keep these HX helpers here;
//! the canonical general toolkit is [`entropyk_core::smoothing`]. See
//! `docs/components/phantom-gradient-regularization.md`.
//!
//! Zero mass flow is a **valid** operating state (circuit staging, isolation, //! Zero mass flow is a **valid** operating state (circuit staging, isolation,
//! Newton trial steps). Hard branches `if |m| < ε { Q = 0 }` create Jacobian //! Newton trial steps). Hard branches `if |m| < ε { Q = 0 }` create Jacobian
//! discontinuities and can leave energy residuals under-ranked. //! discontinuities and can leave energy residuals under-ranked.

220
crates/core/src/smoothing.rs
View File

@@ -24,6 +24,28 @@
//! - [`smooth_abs`] — C^∞ approximation of `|x|`. //! - [`smooth_abs`] — C^∞ approximation of `|x|`.
//! - [`smooth_clamp`] — C¹ clamp into `[lo, hi]`. //! - [`smooth_clamp`] — C¹ clamp into `[lo, hi]`.
//! //!
//! Analytic first derivatives are exported for every Newton-facing primitive
//! ([`smooth_max_derivative`], [`smooth_min_derivative`], [`smooth_abs_derivative`],
//! [`smooth_clamp_derivative`]) so component Jacobians stay exact.
//!
//! # ε / width selection (physical scale of the blend)
//!
//! | Primitive | Parameter | Meaning | Rule of thumb |
//! |---|---|---|---|
//! | [`smooth_abs`] | `eps` | value at `x = 0`; blend half-width | ~1% of characteristic `\|x\|`, or smaller if the kink is far from the operating region |
//! | [`smooth_max`] / [`smooth_min`] | `k` | overshoot at equality = `k / 2` | `k` much smaller than `\|a - b\|` in the region you care about; never so large it shifts equilibrium |
//! | [`smooth_clamp`] | `width` | transition length at each bound | `width <= (hi - lo) / 2`; keep the band physically small (e.g. opening `1e-3`..`1e-2` on `[0, 1]`) |
//!
//! Heat-exchanger mass-flow activity (`flow_activity`, `m_eps`) lives in
//! `entropyk-components` as a specialized reference pattern — see
//! `docs/components/phantom-gradient-regularization.md`.
//!
//! # Degenerate parameters (never panic)
//!
//! - `k <= 0` → hard [`f64::max`] / [`f64::min`]
//! - `eps <= 0` → hard `|x|` / `sign(x)`
//! - `width <= 0` or inverted `[lo, hi]` → hard [`f64::clamp`] (bounds swapped if needed)
//!
//! # Example: smoothing a friction-factor transition //! # Example: smoothing a friction-factor transition
//! //!
//! ```rust //! ```rust
@@ -250,6 +272,8 @@ pub fn quintic_blend_derivative(a: f64, b: f64, x: f64, edge0: f64, edge1: f64)
/// arguments. A small `k` (relative to the scale of `a - b`) gives a sharp but /// arguments. A small `k` (relative to the scale of `a - b`) gives a sharp but
/// still infinitely differentiable maximum. /// still infinitely differentiable maximum.
/// ///
/// When `k <= 0`, returns the hard `a.max(b)` (no panic).
///
/// # Example /// # Example
/// ///
/// ```rust /// ```rust
@@ -259,17 +283,51 @@ pub fn quintic_blend_derivative(a: f64, b: f64, x: f64, edge0: f64, edge1: f64)
/// assert!((smooth_max(5.0, 1.0, 1e-3) - 5.0).abs() < 1e-2); /// assert!((smooth_max(5.0, 1.0, 1e-3) - 5.0).abs() < 1e-2);
/// // Always an upper bound on the true max. /// // Always an upper bound on the true max.
/// assert!(smooth_max(2.0, 2.0, 0.1) >= 2.0); /// assert!(smooth_max(2.0, 2.0, 0.1) >= 2.0);
/// assert_eq!(smooth_max(5.0, 1.0, 0.0), 5.0);
/// ``` /// ```
#[inline] #[inline]
pub fn smooth_max(a: f64, b: f64, k: f64) -> f64 { pub fn smooth_max(a: f64, b: f64, k: f64) -> f64 {
if k <= 0.0 {
return a.max(b);
}
0.5 * (a + b + ((a - b) * (a - b) + k * k).sqrt()) 0.5 * (a + b + ((a - b) * (a - b) + k * k).sqrt())
} }
/// Analytic derivative of [`smooth_max`] with respect to `a` (`b`, `k` fixed).
///
/// Equals `0.5 * (1 + (a - b) / sqrt((a - b)² + k²))` for `k > 0`. When
/// `k <= 0`, returns the hard-max subgradient pick: `1` if `a > b`, `0` if
/// `a < b`, and `0.5` if `a == b`.
///
/// # Example
///
/// ```rust
/// use entropyk_core::smoothing::smooth_max_derivative;
///
/// assert!((smooth_max_derivative(5.0, 1.0, 1e-3) - 1.0).abs() < 1e-2);
/// assert!((smooth_max_derivative(1.0, 5.0, 1e-3)).abs() < 1e-2);
/// ```
#[inline]
pub fn smooth_max_derivative(a: f64, b: f64, k: f64) -> f64 {
if k <= 0.0 {
return if a > b {
1.0
} else if a < b {
0.0
} else {
0.5
};
}
0.5 * (1.0 + (a - b) / ((a - b) * (a - b) + k * k).sqrt())
}
/// C^∞ smooth minimum of `a` and `b` with sharpness controlled by `k > 0`. /// C^∞ smooth minimum of `a` and `b` with sharpness controlled by `k > 0`.
/// ///
/// Uses `0.5 * (a + b - sqrt((a - b)² + k²))`. Always `<= min(a, b)`, converging /// Uses `0.5 * (a + b - sqrt((a - b)² + k²))`. Always `<= min(a, b)`, converging
/// to `min(a, b)` as `k -> 0`. /// to `min(a, b)` as `k -> 0`.
/// ///
/// When `k <= 0`, returns the hard `a.min(b)` (no panic).
///
/// # Example /// # Example
/// ///
/// ```rust /// ```rust
@@ -277,12 +335,44 @@ pub fn smooth_max(a: f64, b: f64, k: f64) -> f64 {
/// ///
/// assert!((smooth_min(5.0, 1.0, 1e-3) - 1.0).abs() < 1e-2); /// assert!((smooth_min(5.0, 1.0, 1e-3) - 1.0).abs() < 1e-2);
/// assert!(smooth_min(2.0, 2.0, 0.1) <= 2.0); /// assert!(smooth_min(2.0, 2.0, 0.1) <= 2.0);
/// assert_eq!(smooth_min(5.0, 1.0, -1.0), 1.0);
/// ``` /// ```
#[inline] #[inline]
pub fn smooth_min(a: f64, b: f64, k: f64) -> f64 { pub fn smooth_min(a: f64, b: f64, k: f64) -> f64 {
if k <= 0.0 {
return a.min(b);
}
0.5 * (a + b - ((a - b) * (a - b) + k * k).sqrt()) 0.5 * (a + b - ((a - b) * (a - b) + k * k).sqrt())
} }
/// Analytic derivative of [`smooth_min`] with respect to `a` (`b`, `k` fixed).
///
/// Equals `0.5 * (1 - (a - b) / sqrt((a - b)² + k²))` for `k > 0`. When
/// `k <= 0`, returns the hard-min subgradient pick: `1` if `a < b`, `0` if
/// `a > b`, and `0.5` if `a == b`.
///
/// # Example
///
/// ```rust
/// use entropyk_core::smoothing::smooth_min_derivative;
///
/// assert!((smooth_min_derivative(1.0, 5.0, 1e-3) - 1.0).abs() < 1e-2);
/// assert!((smooth_min_derivative(5.0, 1.0, 1e-3)).abs() < 1e-2);
/// ```
#[inline]
pub fn smooth_min_derivative(a: f64, b: f64, k: f64) -> f64 {
if k <= 0.0 {
return if a < b {
1.0
} else if a > b {
0.0
} else {
0.5
};
}
0.5 * (1.0 - (a - b) / ((a - b) * (a - b) + k * k).sqrt())
}
/// C^∞ approximation of the absolute value `|x|`. /// C^∞ approximation of the absolute value `|x|`.
/// ///
/// Returns `sqrt(x² + eps²)`. Always `>= |x|`, converging to `|x|` as /// Returns `sqrt(x² + eps²)`. Always `>= |x|`, converging to `|x|` as
@@ -290,6 +380,8 @@ pub fn smooth_min(a: f64, b: f64, k: f64) -> f64 {
/// `x / sqrt(x² + eps²)` is smooth through the origin, replacing the /// `x / sqrt(x² + eps²)` is smooth through the origin, replacing the
/// non-differentiable corner of `|x|` that would otherwise break Newton. /// non-differentiable corner of `|x|` that would otherwise break Newton.
/// ///
/// When `eps <= 0`, returns the hard `|x|` (no panic).
///
/// # Example /// # Example
/// ///
/// ```rust /// ```rust
@@ -298,16 +390,21 @@ pub fn smooth_min(a: f64, b: f64, k: f64) -> f64 {
/// assert!((smooth_abs(0.0, 1e-3) - 1e-3).abs() < 1e-12); /// assert!((smooth_abs(0.0, 1e-3) - 1e-3).abs() < 1e-12);
/// assert!((smooth_abs(5.0, 1e-3) - 5.0).abs() < 1e-3); /// assert!((smooth_abs(5.0, 1e-3) - 5.0).abs() < 1e-3);
/// assert!(smooth_abs(-3.0, 0.1) > 3.0); /// assert!(smooth_abs(-3.0, 0.1) > 3.0);
/// assert_eq!(smooth_abs(-3.0, 0.0), 3.0);
/// ``` /// ```
#[inline] #[inline]
pub fn smooth_abs(x: f64, eps: f64) -> f64 { pub fn smooth_abs(x: f64, eps: f64) -> f64 {
if eps <= 0.0 {
return x.abs();
}
(x * x + eps * eps).sqrt() (x * x + eps * eps).sqrt()
} }
/// Analytic derivative of [`smooth_abs`] with respect to `x`. /// Analytic derivative of [`smooth_abs`] with respect to `x`.
/// ///
/// Equals `x / sqrt(x² + eps²)`, a smooth approximation of `sign(x)` that /// Equals `x / sqrt(x² + eps²)`, a smooth approximation of `sign(x)` that
/// passes continuously through `0` at the origin. /// passes continuously through `0` at the origin. When `eps <= 0`, returns
/// hard `sign(x)` with `0.0` at the origin.
/// ///
/// # Example /// # Example
/// ///
@@ -320,6 +417,15 @@ pub fn smooth_abs(x: f64, eps: f64) -> f64 {
/// ``` /// ```
#[inline] #[inline]
pub fn smooth_abs_derivative(x: f64, eps: f64) -> f64 { pub fn smooth_abs_derivative(x: f64, eps: f64) -> f64 {
if eps <= 0.0 {
return if x > 0.0 {
1.0
} else if x < 0.0 {
-1.0
} else {
0.0
};
}
x / (x * x + eps * eps).sqrt() x / (x * x + eps * eps).sqrt()
} }
@@ -333,6 +439,10 @@ pub fn smooth_abs_derivative(x: f64, eps: f64) -> f64 {
/// always within `[lo, hi]`. For a flat identity region to exist, pass /// always within `[lo, hi]`. For a flat identity region to exist, pass
/// `width <= (hi - lo) / 2`; larger widths still produce a bounded, C¹ result. /// `width <= (hi - lo) / 2`; larger widths still produce a bounded, C¹ result.
/// ///
/// Degenerate cases (never panic):
/// - `hi < lo` → bounds are swapped
/// - `width <= 0` → hard `x.clamp(lo, hi)`
///
/// # Example /// # Example
/// ///
/// ```rust /// ```rust
@@ -343,9 +453,14 @@ pub fn smooth_abs_derivative(x: f64, eps: f64) -> f64 {
/// // Values well outside saturate to the bounds. /// // Values well outside saturate to the bounds.
/// assert!((smooth_clamp(5.0, -1.0, 1.0, 0.1) - 1.0).abs() < 1e-9); /// assert!((smooth_clamp(5.0, -1.0, 1.0, 0.1) - 1.0).abs() < 1e-9);
/// assert!((smooth_clamp(-5.0, -1.0, 1.0, 0.1) + 1.0).abs() < 1e-9); /// assert!((smooth_clamp(-5.0, -1.0, 1.0, 0.1) + 1.0).abs() < 1e-9);
/// assert_eq!(smooth_clamp(5.0, -1.0, 1.0, 0.0), 1.0);
/// ``` /// ```
#[inline] #[inline]
pub fn smooth_clamp(x: f64, lo: f64, hi: f64, width: f64) -> f64 { pub fn smooth_clamp(x: f64, lo: f64, hi: f64, width: f64) -> f64 {
let (lo, hi) = if hi < lo { (hi, lo) } else { (lo, hi) };
if width <= 0.0 {
return x.clamp(lo, hi);
}
// Lower ramp: equals `lo` for x <= lo, eases to identity `x` by x = lo + width. // Lower ramp: equals `lo` for x <= lo, eases to identity `x` by x = lo + width.
// Stays within [lo, x] and is C¹ at both joins (zero slope at lo, unit slope // Stays within [lo, x] and is C¹ at both joins (zero slope at lo, unit slope
// at lo + width). // at lo + width).
@@ -354,6 +469,36 @@ pub fn smooth_clamp(x: f64, lo: f64, hi: f64, width: f64) -> f64 {
hi + (lower - hi) * smoothstep(hi, hi - width, lower) hi + (lower - hi) * smoothstep(hi, hi - width, lower)
} }
/// Analytic derivative of [`smooth_clamp`] with respect to `x`.
///
/// Chain-rules the lower then upper [`smoothstep`] ramps. Outside the
/// transition bands the slope is `0` (saturated) or `1` (identity interior).
/// Degenerate parameters match [`smooth_clamp`]: hard-clamp derivative is `1`
/// on the open interior and `0` elsewhere (including the kink points).
///
/// # Example
///
/// ```rust
/// use entropyk_core::smoothing::smooth_clamp_derivative;
///
/// // Flat exterior, unit slope deep interior.
/// assert!((smooth_clamp_derivative(5.0, -1.0, 1.0, 0.1)).abs() < 1e-9);
/// assert!((smooth_clamp_derivative(0.0, -1.0, 1.0, 0.1) - 1.0).abs() < 1e-9);
/// ```
#[inline]
pub fn smooth_clamp_derivative(x: f64, lo: f64, hi: f64, width: f64) -> f64 {
let (lo, hi) = if hi < lo { (hi, lo) } else { (lo, hi) };
if width <= 0.0 {
return if x > lo && x < hi { 1.0 } else { 0.0 };
}
let s_lo = smoothstep(lo, lo + width, x);
let d_lower = s_lo + (x - lo) * smoothstep_derivative(lo, lo + width, x);
let lower = lo + (x - lo) * s_lo;
let s_hi = smoothstep(hi, hi - width, lower);
let ds_hi = smoothstep_derivative(hi, hi - width, lower);
d_lower * (s_hi + (lower - hi) * ds_hi)
}
#[cfg(test)] #[cfg(test)]
mod tests { mod tests {
use super::*; use super::*;
@@ -528,15 +673,84 @@ mod tests {
#[test] #[test]
fn test_smooth_max_derivative_matches_fd() { fn test_smooth_max_derivative_matches_fd() {
// d/da smooth_max = 0.5 * (1 + (a-b)/sqrt((a-b)^2 + k^2))
let (b, k): (f64, f64) = (1.0, 0.3); let (b, k): (f64, f64) = (1.0, 0.3);
for a in [-1.0, 0.5, 1.0, 1.5, 3.0] { for a in [-1.0, 0.5, 1.0, 1.5, 3.0] {
let analytic = 0.5 * (1.0 + (a - b) / ((a - b) * (a - b) + k * k).sqrt()); let analytic = smooth_max_derivative(a, b, k);
let numeric = fd(|a| smooth_max(a, b, k), a, 1e-6); let numeric = fd(|a| smooth_max(a, b, k), a, 1e-6);
assert!((analytic - numeric).abs() < 1e-5, "at a={}", a); assert!((analytic - numeric).abs() < 1e-5, "at a={}", a);
} }
} }
#[test]
fn test_smooth_min_derivative_matches_fd() {
let (b, k): (f64, f64) = (1.0, 0.3);
for a in [-1.0, 0.5, 1.0, 1.5, 3.0] {
let analytic = smooth_min_derivative(a, b, k);
let numeric = fd(|a| smooth_min(a, b, k), a, 1e-6);
assert!((analytic - numeric).abs() < 1e-5, "at a={}", a);
}
}
#[test]
fn test_smooth_clamp_derivative_matches_fd() {
let (lo, hi, width) = (-1.0, 1.0, 0.1);
// Exterior, both ramps, deep interior.
for x in [-5.0, -1.05, -0.95, -0.5, 0.0, 0.5, 0.95, 1.05, 5.0] {
let analytic = smooth_clamp_derivative(x, lo, hi, width);
let numeric = fd(|x| smooth_clamp(x, lo, hi, width), x, 1e-6);
assert!(
(analytic - numeric).abs() < 1e-5,
"smooth_clamp deriv mismatch at {}: {} vs {}",
x,
analytic,
numeric
);
}
}
#[test]
fn test_smooth_clamp_c1_at_junctions() {
// Slope continuity across the four joins: lo, lo+width, hi-width, hi.
let (lo, hi, width) = (-1.0, 1.0, 0.2);
let junctions = [lo, lo + width, hi - width, hi];
let h = 1e-5;
for j in junctions {
let slope_left = fd(|x| smooth_clamp(x, lo, hi, width), j - h, h);
let slope_right = fd(|x| smooth_clamp(x, lo, hi, width), j + h, h);
let analytic = smooth_clamp_derivative(j, lo, hi, width);
assert!(
(slope_left - slope_right).abs() < 5e-3,
"slope jump at {}: left={} right={}",
j,
slope_left,
slope_right
);
assert!(
(analytic - 0.5 * (slope_left + slope_right)).abs() < 5e-3,
"analytic slope mismatch at {}: analytic={} fd_avg={}",
j,
analytic,
0.5 * (slope_left + slope_right)
);
}
}
#[test]
fn test_degenerate_parameters_do_not_panic() {
assert_eq!(smooth_max(3.0, 1.0, 0.0), 3.0);
assert_eq!(smooth_max(3.0, 1.0, -0.5), 3.0);
assert_eq!(smooth_min(3.0, 1.0, -1.0), 1.0);
assert_eq!(smooth_abs(-2.0, 0.0), 2.0);
assert_eq!(smooth_abs_derivative(-2.0, 0.0), -1.0);
assert_eq!(smooth_clamp(5.0, -1.0, 1.0, 0.0), 1.0);
assert_eq!(smooth_clamp_derivative(0.0, -1.0, 1.0, 0.0), 1.0);
assert_eq!(smooth_clamp_derivative(5.0, -1.0, 1.0, 0.0), 0.0);
// Inverted bounds swap.
assert!((smooth_clamp(0.0, 1.0, -1.0, 0.1) - 0.0).abs() < 1e-9);
assert_eq!(smooth_max_derivative(3.0, 1.0, 0.0), 1.0);
assert_eq!(smooth_min_derivative(3.0, 1.0, 0.0), 0.0);
}
#[test] #[test]
fn test_smooth_abs_properties_and_derivative() { fn test_smooth_abs_properties_and_derivative() {
assert!((smooth_abs(0.0, 1e-3) - 1e-3).abs() < 1e-12); assert!((smooth_abs(0.0, 1e-3) - 1e-3).abs() < 1e-12);

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@@ -0,0 +1,148 @@
# Jacobian-Killing Pattern Audit
**Date:** 2026-07-18
**Story:** `0-1-jacobian-killing-pattern-audit-fd-test-harness` (Epic 0)
**Scope:** Inventory of `clamp` / `max` / `min` (and related hard gates) on Newton residual/Jacobian paths in `entropyk-components`. Physics fixes are owned by Stories 0.2–0.4.
## Failure-mode legend
| Mode | Meaning |
|------|---------|
| `zero-gradient` | Analytic ∂r/∂x (or helper derivative) hard-zeros in a region where physics should still inform Newton |
| `discontinuity` | Hard clamp/step on a Newton unknown → C⁰ or worse residual; FD and analytic disagree near the edge |
| `benign` | Floor/guard for division-by-zero, config validation, or non-Newton parameter — not a solver killer |
| `already-regularized` | C¹ / phantom pattern already present (may still need unification) |
| Severity | Meaning |
|----------|---------|
| `P0` | Confirmed FR19 killer; blocks convergence at domain edges |
| `P1` | Likely Newton-relevant clamp on live unknowns / quality |
| `P2` | Secondary / correlation-local; watch when that path is active |
| `info` | Documented debt or missing API; not a clamp site |
---
## FR19 known-bad sites (confirmed 2026-07-18)
| Site | Failure mode | Severity | Fix owner |
|------|--------------|----------|-----------|
| `crates/components/src/valve_flow.rs:105-107` — `valve_mass_flow_dp_up` returns `Ok(0.0)` when `dp <= 0 \|\| m <= 0` | `zero-gradient` | **P0** | Story 0.3 |
| `crates/components/src/isenthalpic_expansion_valve.rs:233` — `state[i].clamp(0.0, 1.0)` on orifice opening (residual path) | `discontinuity` | **P0** | Story 0.3 |
| `crates/components/src/isenthalpic_expansion_valve.rs:449` — `_state[i].clamp(0.0, 1.0)` on orifice opening (Jacobian path) | `discontinuity` | **P0** | Story 0.3 |
| `crates/components/src/heat_exchanger/two_phase_dp.rs:107` — `quality.clamp(0.0, 1.0)` in `homogeneous_density` | `discontinuity` | **P0** | Story 0.4 |
| `crates/components/src/heat_exchanger/two_phase_dp.rs:150` — `quality.clamp(0.0, 1.0)` in `friedel_multiplier` | `discontinuity` | **P0** | Story 0.4 |
| `crates/components/src/heat_exchanger/condenser.rs:492` — `state[idx].clamp(0.0, 1.5)` fan actuator φ | `discontinuity` | **P0** | Story 0.4 |
| `crates/components/src/heat_exchanger/condenser.rs:752` — `state[idx].clamp(0.0, 0.98)` flooded level λ | `discontinuity` | **P0** | Story 0.4 |
### Evidence notes
- **Valve ΔP≤0:** `valve_mass_flow` already forces `dp = ΔP.max(0)`, so ṁ=0 and `valve_mass_flow_dp_up` returns a hard zero — Newton gets no direction to restore positive ΔP.
- **EXV opening clamps:** same hard clamp appears in both residual helper and Jacobian branch; Story 0.2 `smooth_clamp` is the intended replacement (`entropyk_core::smoothing` already exists).
- **EXV phantom ΔP:** `DP_FLOOR` (~L396–445) is a **partial** `already-regularized` mitigation for ΔP≤0 on the Jacobian only; residual still early-outs. Opening clamps remain P0.
- **Missing API:** Epic Story 0.3 text mentions `valve_mass_flow_dp_down` — **only `valve_mass_flow_dp_up` exists** today (`lib.rs` re-export). Catalogue gap severity `info`; inventing `dp_down` is out of scope for Story 0.1.
---
## Broader catalogue (residual / Jacobian call graph)
Classified from a ripgrep sweep of `.clamp(` / `.max(` / `.min(` under `crates/components/src`. Not every hit is listed — config setters, test helpers, and pure numerical floors are collapsed into summary rows.
### P0 / P1 — Newton-relevant
| Location | Pattern | Mode | Sev | Notes / owner |
|----------|---------|------|-----|---------------|
| `valve_flow.rs:71,75,78,99` | `dp.max(0)`, `opening.clamp`, `m.max(0)` | `zero-gradient` / `discontinuity` | P0 | Feeds EXV/orifice; Story 0.3 |
| `valve_flow.rs:105-107` | hard `Ok(0.0)` on ∂ṁ/∂P_up | `zero-gradient` | P0 | FR19 |
| `isenthalpic_expansion_valve.rs:233,449` | opening clamp on state | `discontinuity` | P0 | FR19 → 0.3 |
| `isenthalpic_expansion_valve.rs:396-445` | `DP_FLOOR` phantom | `already-regularized` | info | Keep; unify with toolkit in 0.2/0.3 |
| `two_phase_dp.rs:107,150` | quality clamp | `discontinuity` | P0 | FR19 → 0.4 |
| `two_phase_dp.rs:118-131` | hard `x<=0` / `x>=1` branches in `zivi_void_fraction` | `discontinuity` | P1 | Story 0.4 (MSH/dome) |
| `two_phase_dp.rs:255-294` | Hermite blend near x→1 (`msh_gradient`) | `already-regularized` | info | Partial MSH fix; 0.4 completes |
| `condenser.rs:492,752` | fan / flood actuator clamps | `discontinuity` | P0 | FR19 → 0.4 |
| `evaporator.rs` | analogous secondary / property floors | `benign` / P2 | P2 | Re-check when evaporator actuators mirror condenser |
| `heat_exchanger/flow_regularization.rs` | smooth mass / activity | `already-regularized` | info | Reference for Story 0.2 unification |
| `heat_exchanger/sat_domain.rs:81` | `p_pa.clamp(p_min, p_max)` | `discontinuity` | P1 | Intermediate iterate domain; Story 0.4 / sat path |
| `screw_economizer_compressor.rs:486` | eco fraction `.clamp(0.0, 0.4)` | `discontinuity` | P1 | If eco fraction is a Newton unknown |
| `screw_economizer_compressor.rs:291,343` | slide valve clamp | `discontinuity` | P1 | Config vs state — verify call site |
| `bphx_correlation.rs:588+` | quality / p_reduced clamps | `discontinuity` | P2 | Correlation internals on quality |
### Benign / info (not Epic-0 P0)
| Pattern class | Examples | Mode | Sev |
|---------------|----------|------|-----|
| Divisor floors | `.max(1e-9)`, `.max(1e-12)` on ρ, μ, D | `benign` | info |
| Builder / config clamps | `with_orifice_fixed` opening clamp, UA scale `.max(0)` | `benign` | info |
| Registry JSON parsing | `registry.rs` quality/RH clamps | `benign` | info |
| Air humidity RH clamp | `air_boundary.rs` | `benign` | info |
| FD step sizing in tests | `(x.abs()*1e-6).max(1e-3)` | `benign` | info |
### Related NFR9 debt (not clamp killers — do not fix in 0.1–0.4 regularization stories)
| Item | Issue | Sev |
|------|-------|-----|
| `heat_exchanger/exchanger.rs:854-897` | 4-port Jacobian is **100% central FD** in production | info (NFR9) |
| `screw_economizer_compressor.rs` | Incomplete analytic Jacobian rows | info |
| `python_components.rs` | Empty `jacobian_entries` stubs | info |
| Category-B solver tests (`jacobian_freezing`, inverse calibration) | Deferred per `plans/audit-2026-07-remediation-plan.md` | info |
---
## Harness usage (`entropyk_components::jacobian_fd`)
Central FD vs analytic at one state point:
```rust
use entropyk_components::jacobian_fd::{
check_jacobian_health, JacobianFdConfig,
};
let report = check_jacobian_health(&component, &state, JacobianFdConfig::default())?;
assert!(
report.has_zero_gradient_killers(),
"expected clamp/zero-gradient signature, got clean report"
);
// After Stories 0.2–0.4 fixes, Story 0.5 flips the gate to:
// assert!(report.is_clean());
```
### Defaults (aligned with condenser FD tests)
| Constant | Default |
|----------|---------|
| `rel_epsilon` | `1e-6` |
| `h_floor` | `1e-3` |
| `rel_tol` | `1e-4` |
| `analytic_atol` | `1e-12` |
| `fd_informative` | `1e-8` |
**Do not** call `JacobianMatrix::numerical` (solver) from this harness — that API is **forward** difference for Newton fallback.
Integration smoke tests: `crates/components/tests/jacobian_health_sweep.rs`.
---
## Story 0.5 CI gate (future)
1. Reuse `check_jacobian_health` over per-component physical-domain grids (ΔP≤0, quality 0/1, opening 0/1, dome edges, actuator clamps).
2. Fail CI on new `zero_gradient_killers` or mismatches outside an allow-list that shrinks to empty after 0.2–0.4.
3. Commit a per-component / per-region health report artifact (extend this file or generate JSON beside it).
---
## Deferred work (explicit)
| Work | Owner |
|------|-------|
| Standardize / document `smooth_*` ε guidance; declare `flow_regularization` as HX reference | Story **0.2** — **landed** (`docs/components/phantom-gradient-regularization.md`; derivatives in `crates/core/src/smoothing.rs`) |
| Valve ΔP≤0 phantom + EXV opening `smooth_clamp` | Story **0.3** |
| Quality / condenser–evaporator state clamps + MSH singularity | Story **0.4** |
| Full-envelope CI Jacobian health gate | Story **0.5** |
| Replace production FD Jacobian in generic 4-port HX | Separate NFR9 / remediation track |
---
## Severity ranking summary
1. **P0 (fix in 0.3–0.4):** valve ΔP zero-gradient; EXV opening clamps; two-phase quality clamps; condenser fan/flood clamps.
2. **P1:** sat-domain pressure clamp; screw eco/slide clamps when unknowns; zivi hard edges.
3. **P2 / info:** correlation floors, config clamps, NFR9 FD-in-production debt.

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# Flow regularization (zero-flow helpers)
Source: `crates/components/src/heat_exchanger/flow_regularization.rs`
Used by: **FloodedEvaporator** (full residual path); **Condenser** / **Evaporator** (smooth `|ṁ|` for live `C_sec`).
> **Standard:** This module is the **reference specialized pattern** for HX
> zero-flow residuals. The canonical general C¹ toolkit is
> `entropyk_core::smoothing` — see
> [phantom-gradient-regularization.md](./phantom-gradient-regularization.md).
> Do not move these helpers into core; do not duplicate `smooth_*` here.
---
## EN
### Why
Zero mass flow is a **valid** state (staging, circuit off, Newton trial steps). Hard branches like `if |m| < ε { Q = 0 }` create **Jacobian discontinuities**.
### API
| Function | Meaning |
|----------|---------|
| `flow_activity(m, ε)` | α = m²/(m²+ε²) ∈ [0,1), α(0)=0 |
| `flow_activity_derivative` | dα/dm |
| `effective_duty(Q, α_a, α_b)` | Q_eff = α_a · α_b · Q |
| `blend_transport_residual` | blend active transport residual with Δh hold |
| `blend_transport_partials` | analytic partials of the blend |
| `smooth_mass_magnitude` | C¹-ish smooth \|m\| for `C = \|ṁ\| · cp` |
| `smooth_mass_magnitude_derivative` | d\|m\|_smooth / dm |
Defaults: `DEFAULT_M_EPS_KG_S = 1e-4`, `DEFAULT_M_SCALE_KG_S = 0.05`.
### Interaction with rating mode (Flooded)
On **FloodedEvaporator system path** (live secondary): duty uses `effective_duty` with α_ref and α_sec.
On **Flooded rating path** (scalar C_sec only): residual energy uses **full Q** (no α_ref gate) so `ṁ_ref = 0` is not a trivial root when `C_sec > 0`.
### DoF rule
Regularization **must not** change `n_equations()`. It only reshapes residual values and derivatives.
---
## FR
### Pourquoi
Le débit nul est un état **valide**. Les `if |m| < ε` durs cassent le Newton.
### API
Voir le tableau EN.
### Rating vs système (Flooded)
- **Système (ports live)** : duty régularisée α_ref · α_sec · Q.
- **Rating (scalaires)** : Q **plein** dans le résidu énergie (pas de racine triviale ṁ=0).
### Règle DoF
La régularisation **ne change pas** `n_equations()`.

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# Phantom-Gradient Regularization Standard
Canonical toolkit for C¹ (or smoother) replacements of hard clamps, `max`/`min`,
and absolute-value kinks on Newton unknowns. Owned by Epic 0 / Story 0.2
(`epics-solver-hp.md`, FR19).
Source code: `crates/core/src/smoothing.rs` (`entropyk_core::smoothing`).
---
## Decisions
| Layer | Location | Role |
|-------|----------|------|
| **Canonical general toolkit** | `entropyk_core::smoothing` | `smooth_max` / `smooth_min` / `smooth_abs` / `smooth_clamp` (+ analytic derivatives) |
| **Reference specialized pattern** | `heat_exchanger::flow_regularization` | Mass-flow activity / duty / transport blend for zero-flow HX residuals — **not** duplicated into core |
| **Verification harness** | `entropyk_components::jacobian_fd` | Central FD vs analytic (Story 0.1); CI gate is Story 0.5 |
**Banned** in residual / Jacobian paths on Newton unknowns:
- bare `.clamp(...)` whose derivative jumps `0 ↔ 1`
- hard `.max(0)` / early `Ok(0.0)` that zeros informative physics derivatives
Physical clamp → smooth migrations are Stories **0.3** (valve / EXV) and **0.4** (HX).
This standard ships toolkit + docs only; it does not change component physics.
DoF rule: regularization **must not** change `n_equations()`.
---
## API (core)
| Function | Continuity | Parameter |
|----------|------------|-----------|
| `smooth_max(a, b, k)` / `smooth_max_derivative` | C∞ | sharpness `k` (overshoot at equality = `k/2`) |
| `smooth_min(a, b, k)` / `smooth_min_derivative` | C∞ | same |
| `smooth_abs(x, eps)` / `smooth_abs_derivative` | C∞ | `eps` = value at `x=0` |
| `smooth_clamp(x, lo, hi, width)` / `smooth_clamp_derivative` | C¹ | transition `width` at each bound |
| `smoothstep` / `cubic_blend` / `quintic_blend` (+ derivatives) | C¹ / C² | correlation transition windows |
Degenerate parameters never panic: `k <= 0` → hard max/min; `eps <= 0` → hard `|x|`;
`width <= 0` or inverted bounds → hard clamp (bounds swapped if needed).
---
## ε / width selection guidance
| Primitive | Parameter | Physical meaning | Rule of thumb |
|-----------|-----------|------------------|---------------|
| `smooth_abs` | `eps` | Blend half-width; value at origin | ~1% of characteristic `\|x\|`, or smaller if the kink is far from the operating region |
| `smooth_max` / `smooth_min` | `k` | Softness; overshoot at equality = `k/2` | `k ≪ \|a − b\|` where you need the hard extremum; never large enough to shift equilibrium |
| `smooth_clamp` | `width` | Transition length at each bound | Prefer `width ≤ (hi − lo) / 2`. Keep Newton-visible band physically small |
| `flow_activity` | `m_eps` | Mass-flow activity scale | Keep HX default `DEFAULT_M_EPS_KG_S = 1e-4` (see [flow-regularization.md](./flow-regularization.md)) |
### Recommended starting widths (examples only)
| Quantity | Interval | Suggested `width` |
|----------|----------|-------------------|
| Valve / EXV opening | `[0, 1]` | `1e-3` … `1e-2` |
| Thermodynamic quality | `[0, 1]` | `1e-3` … `1e-2` |
| Fan actuator | `[0, 1.5]` | `~1e-2` |
| Flood level | `[0, 0.98]` | `~1e-2` (respect `width ≤ (hi−lo)/2`) |
Always pair value and derivative in both `compute_residuals` and `jacobian_entries`
(`smooth_clamp` + `smooth_clamp_derivative`, etc.).
---
## Relationship to flow regularization
`crates/components/src/heat_exchanger/flow_regularization.rs` is the **reference
implementation** for zero-flow-safe HX residuals. It builds on
`entropyk_core::smoothing::smooth_abs` and stays in `entropyk-components` because
it encodes residual units (watts) and characteristic mass-flow scales
(`m_scale`) that are HX-specific.
Do **not** move `flow_activity` / `blend_transport_residual` into core.
Do **not** invent a second smoothing module under `components/`.
Details: [flow-regularization.md](./flow-regularization.md).
---
## Verification
- Unit / FD continuity tests: `crates/core/src/smoothing.rs` (`#[cfg(test)]`).
- Component Jacobian health: `check_jacobian_health` (Story 0.1 audit harness).
- Envelope CI gate: Story 0.5.