Entropyk/_bmad-output/implementation-artifacts/4-7-convergence-criteria-and-validation.md

Story 4.7: Convergence Criteria & Validation

Status: done

Story

As a simulation user, I want strict, multi-dimensional convergence criteria with per-circuit granularity and a sparse/block-diagonal Jacobian for multi-circuit systems, so that large systems remain tractable and convergence is only declared when ALL circuits physically satisfy pressure, mass, and energy balances simultaneously.

Acceptance Criteria

1. Δ Pressure convergence ≤ 1 Pa (AC: #1)

   • Given a system approaching solution
   • When checking convergence with ConvergenceCriteria::check()
   • Then the check passes only if max |ΔP_i| < 1.0 Pa across all pressure state variables
   • And a configurable pressure_tolerance_pa: f64 field (default 1.0 Pa) controls the threshold

2. Mass balance error < 1e-9 kg/s per circuit (AC: #2)

   • Given a cycle residuals vector
   • When ConvergenceCriteria::check() is called
   • Then mass balance error per circuit is extracted: Σ |ṁ_in - ṁ_out| < 1e-9 kg/s
   • And mass_balance_tolerance_kgs: f64 field (default 1e-9) controls the threshold

3. Energy balance error < 1e-6 kW per circuit (AC: #3)

   • Given a cycle residuals vector
   • When ConvergenceCriteria::check() is called
   • Then energy balance error per circuit satisfies |Σ Q̇ + Ẇ - Σ (ṁ·h)| < 1e-6 kW (1e-3 W)
   • And energy_balance_tolerance_w: f64 field (default 1e-3) controls the threshold

4. Per-circuit convergence tracking (AC: #4)

   • Given a multi-circuit system (N circuits)
   • When checking convergence
   • Then ConvergenceReport contains a per_circuit: Vec<CircuitConvergence> with one entry per active circuit
   • And each CircuitConvergence contains: circuit_id: u8, pressure_ok: bool, mass_ok: bool, energy_ok: bool, converged: bool
   • And circuit.converged = pressure_ok && mass_ok && energy_ok

5. Global convergence = ALL circuits converged (AC: #5)

   • Given a multi-circuit system with N circuits
   • When ConvergenceReport::is_globally_converged() is called
   • Then it returns true if and only if ALL entries in per_circuit have converged == true
   • And a single-circuit system behaves identically (degenerate case of N=1)

6. Block-diagonal Jacobian for uncoupled multi-circuit (AC: #6)

   • Given a system with N circuits that have NO thermal couplings between them
   • When JacobianMatrix is assembled via system.assemble_jacobian()
   • Then the resulting matrix has block-diagonal structure (entries outside circuit blocks are zero)
   • And JacobianMatrix::block_structure(system) returns Vec<(row_start, row_end, col_start, col_end)> describing each circuit block
   • And JacobianMatrix::is_block_diagonal(system, tolerance: f64) returns true for uncoupled systems

7. ConvergenceCriteria integrates with solvers (AC: #7)

   • Given a NewtonConfig or PicardConfig
   • When the user sets solver.with_convergence_criteria(criteria)
   • Then the solver uses ConvergenceCriteria::check() instead of the raw L2-norm tolerance check
   • And the old tolerance: f64 field remains for backward-compat (ignored when convergence_criteria is Some)
   • And FallbackSolver delegates with_convergence_criteria() to both sub-solvers

8. ConvergenceReport in ConvergedState (AC: #8)

   • Given a converged system
   • When ConvergedState is returned
   • Then it optionally contains convergence_report: Option<ConvergenceReport>
   • And ConvergedState::convergence_report() returns None when criteria is not set (backward-compat)

Tasks / Subtasks

• Create crates/solver/src/criteria.rs module (AC: #1–#6)

  • Define ConvergenceCriteria struct with fields:
    • pressure_tolerance_pa: f64 (default 1.0)
    • mass_balance_tolerance_kgs: f64 (default 1e-9)
    • energy_balance_tolerance_w: f64 (default 1e-3)
  • Implement ConvergenceCriteria::default() using the values above
  • Define CircuitConvergence struct: circuit_id: u8, pressure_ok: bool, mass_ok: bool, energy_ok: bool, converged: bool
  • Define ConvergenceReport struct: per_circuit: Vec<CircuitConvergence>, globally_converged: bool
  • Implement ConvergenceReport::is_globally_converged() -> bool
  • Implement ConvergenceCriteria::check(state: &[f64], residuals: &[f64], system: &System) -> ConvergenceReport:
    • Extract per-circuit pressure deltas from state vector using system.circuit_edges(circuit_id) and system.edge_state_indices(edge)
    • For each circuit: compute max |ΔP| < pressure_tolerance_pa (use state increments from previous Newton step if available, else use residuals as proxy)
    • For each circuit: compute mass balance residual sum < mass_balance_tolerance_kgs
    • For each circuit: compute energy balance residual sum < energy_balance_tolerance_w
    • Return ConvergenceReport with per-circuit and global status
  • Expose criteria.rs in lib.rs (AC: #7)

• Add block_structure support to JacobianMatrix (AC: #6)

  • Implement JacobianMatrix::block_structure(system: &System) -> Vec<(usize, usize, usize, usize)> (row_start, row_end, col_start, col_end per circuit)
  • Implement JacobianMatrix::is_block_diagonal(system: &System, tolerance: f64) -> bool — verify off-block entries are < tolerance
  • These are pure analysis helpers; they do NOT change how the Jacobian is built (nalgebra DMatrix<f64> is retained)

• Integrate ConvergenceCriteria into solvers (AC: #7, #8)

  • Add convergence_criteria: Option<ConvergenceCriteria> field to NewtonConfig
  • Add with_convergence_criteria(mut self, criteria: ConvergenceCriteria) -> Self builder to NewtonConfig
  • In NewtonConfig::solve(): if convergence_criteria.is_some(), call criteria.check() for convergence test instead of raw current_norm < self.tolerance
  • Same pattern for PicardConfig
  • Add with_convergence_criteria() to FallbackSolver (delegates to both)
  • Add convergence_report: Option<ConvergenceReport> to ConvergedState
  • Update ConvergedState::new() or add ConvergedState::with_report() constructor

• Expose everything in lib.rs

  • pub mod criteria;
  • Re-export: ConvergenceCriteria, ConvergenceReport, CircuitConvergence

• Unit tests in criteria.rs (AC: #1–#5)

  • test_default_thresholds: assert ConvergenceCriteria::default() has correct values (1.0, 1e-9, 1e-3)
  • test_single_circuit_converged: 2-edge single-circuit system with zero residuals → globally_converged = true
  • test_single_circuit_not_converged_pressure: residuals indicating ΔP = 2 Pa → pressure_ok = false
  • test_multi_circuit_global_needs_all: 2-circuit system, circuit 0 converged, circuit 1 not → is_globally_converged() = false
  • test_multi_circuit_all_converged: 2-circuit system, both converged → is_globally_converged() = true
  • test_custom_thresholds: custom pressure_tolerance_pa = 0.1 → tighter convergence check

• Unit tests in jacobian.rs (AC: #6)

  • test_block_structure_single_circuit: single circuit → one block covering full matrix
  • test_block_structure_two_circuits: 2 uncoupled circuits → 2 blocks, no overlap
  • test_is_block_diagonal_uncoupled: build uncoupled 2-circuit system, assert is_block_diagonal(system, 1e-10) = true
  • test_is_block_diagonal_coupled: manually add off-block entries, assert is_block_diagonal(...) = false

• Integration test in crates/solver/tests/convergence_criteria.rs

  • test_newton_with_criteria_single_circuit: Newton solver + ConvergenceCriteria::default() on 2-edge system, assert is_globally_converged = true in report
  • test_newton_with_criteria_backward_compat: Newton solver without convergence_criteria set, assert convergence_report = None in ConvergedState

Dev Notes

Epic Context

Epic 4: Intelligent Solver Engine — Solve any system with < 1s guarantee, Newton-Raphson ↔ Sequential Substitution fallback.

Story Dependencies (all DONE):

• Story 4.1 — Solver trait, SolverError, ConvergedState, ConvergenceStatus defined
• Story 4.2 — Full Newton with line search, NewtonConfig
• Story 4.3 — Picard with relaxation, PicardConfig
• Story 4.4 — FallbackSolver with Newton↔Picard switching
• Story 4.5 — TimeoutConfig, best-state tracking, ZOH (adds previous_state, timeout_config to configs)
• Story 4.6 — SmartInitializer, initial_state field added to NewtonConfig/PicardConfig/FallbackSolver
• Story 4.8 (NEXT) — Jacobian Freezing Optimization

FRs covered:

• FR20 — Convergence criterion: max |ΔP| < 1 Pa (1e-5 bar)
• FR21 — Global multi-circuit convergence: ALL circuits must converge

Architecture Context

Technical Stack:

• entropyk_core::{Pressure, Temperature, Enthalpy, MassFlow} — NewType wrappers (MUST use in public API, no bare f64)
• nalgebra::DMatrix<f64> — backing type of JacobianMatrix (already in jacobian.rs)
• tracing — structured logging (already in solver crate)
• thiserror — error handling (already in solver crate)
• approx — assert_relative_eq! for float tests (already in dev-dependencies)

Existing Infrastructure to Leverage:

// crates/solver/src/system.rs — EXISTING
pub struct System {
    node_to_circuit: HashMap<NodeIndex, CircuitId>,  // node → circuit
    thermal_couplings: Vec<ThermalCoupling>,  // inter-circuit heat transfer
    // ...
}

impl System {
    pub fn circuit_count(&self) -> usize { ... }  // distinct circuit IDs
    pub fn circuit_edges(&self, circuit_id: CircuitId) -> impl Iterator<Item=EdgeIndex> + '_ { ... }
    pub fn edge_circuit(&self, edge: EdgeIndex) -> CircuitId { ... }
    pub fn edge_state_indices(&self, edge_id: EdgeIndex) -> (usize, usize)  // (p_idx, h_idx)
    pub fn circuit_nodes(&self, circuit_id: CircuitId) -> impl Iterator<Item=NodeIndex> + '_ { ... }
    pub fn state_vector_len(&self) -> usize { ... }  // 2 * edge_count
    pub fn thermal_coupling_count(&self) -> usize { ... }  // number of couplings
}

// State vector layout: [P_edge0, h_edge0, P_edge1, h_edge1, ...]
// Pressure entries: state[2*i], Enthalpy entries: state[2*i + 1]

// crates/solver/src/solver.rs — EXISTING (post Story 4.6)
pub struct NewtonConfig {
    pub max_iterations: usize,        // default 100
    pub tolerance: f64,               // default 1e-6 (keep for backward-compat)
    pub line_search: bool,
    pub timeout: Option<Duration>,
    pub use_numerical_jacobian: bool,
    pub line_search_armijo_c: f64,
    pub line_search_max_backtracks: usize,
    pub divergence_threshold: f64,
    pub timeout_config: TimeoutConfig,
    pub previous_state: Option<Vec<f64>>,
    pub initial_state: Option<Vec<f64>>,
    // ADD: pub convergence_criteria: Option<ConvergenceCriteria>,
}

pub struct PicardConfig {
    pub max_iterations: usize,
    pub tolerance: f64,               // keep for backward-compat
    pub relaxation_factor: f64,
    pub timeout: Option<Duration>,
    pub divergence_threshold: f64,
    pub divergence_patience: usize,
    pub timeout_config: TimeoutConfig,
    pub previous_state: Option<Vec<f64>>,
    pub initial_state: Option<Vec<f64>>,
    // ADD: pub convergence_criteria: Option<ConvergenceCriteria>,
}

pub struct ConvergedState {
    pub state: Vec<f64>,
    pub iterations: usize,
    pub final_residual: f64,
    pub status: ConvergenceStatus,
    // ADD: pub convergence_report: Option<ConvergenceReport>,
}

// Currently in NewtonConfig::solve():
// if current_norm < self.tolerance → converged
// CHANGE TO: if let Some(ref c) = self.convergence_criteria { c.check(...).is_globally_converged() }
//            else { current_norm < self.tolerance }

crates/solver/src/jacobian.rs — EXISTING:

pub struct JacobianMatrix(DMatrix<f64>);

impl JacobianMatrix {
    pub fn from_builder(entries: &[(usize, usize, f64)], n_rows: usize, n_cols: usize) -> Self { ... }
    pub fn solve(&self, residuals: &[f64]) -> Option<Vec<f64>> { ... }
    pub fn numerical<F>(...) -> Self { ... }
    pub fn as_matrix(&self) -> &DMatrix<f64> { ... }
    pub fn nrows(&self) -> usize { ... }
    pub fn ncols(&self) -> usize { ... }
    pub fn get(&self, row: usize, col: usize) -> Option<f64> { ... }
    pub fn set(&mut self, row: usize, col: usize, value: f64) { ... }
    pub fn norm(&self) -> f64 { ... }
    pub fn condition_number(&self) -> Option<f64> { ... }
    // ADD:
    // pub fn block_structure(&self, system: &System) -> Vec<(usize, usize, usize, usize)>
    // pub fn is_block_diagonal(&self, system: &System, tolerance: f64) -> bool
}

ConvergenceCriteria::check() Implementation Guide:

The key challenge is mapping the residual vector back to per-circuit quantities. The residual vector is assembled in component order (same order as traverse_for_jacobian()). For now, the simplest approach that meets the AC:

1. Pressure check: For each circuit, iterate system.circuit_edges(circuit_id). For each edge, extract (p_idx, _) = system.edge_state_indices(edge). Compute |state[p_idx] - prev_state[p_idx]| if previous state available, or use the residuals at those indices as a proxy (residuals ≈ pressure errors at convergence).

2. Mass/Energy balance: The convergence check needs mass and energy residuals per circuit. The simplest AC-compliant implementation:

   • When ConvergenceCriteria is used, the solver passes the full residual vector
   • The check partitions residuals by circuit using the equation ordering from compute_residuals() (same as traverse_for_jacobian())
   • For mass: residuals with unit Pa (pressure continuity) at convergence are near 0; use residual norm per circuit < threshold
   • NOTE: A fully correct mass/energy extraction requires component-level metadata that doesn't exist yet. For Story 4-7, use a pragmatic approach: treat the residual norm per circuit as the mass/energy proxy. Full mass/energy balance validation is Epic 7 (Stories 7-1, 7-2). Document this clearly in criteria.rs.

3. Block structure: For block_structure(system), iterate each circuit ID 0..circuit_count. For each circuit, find the range of state column indices (from edge_state_indices) and the range of equation rows (from traverse_for_jacobian() filtered by circuit). Return (row_start, row_end, col_start, col_end) per circuit.

ConvergenceCriteria::check() Signature:

/// Result of convergence checking, broken down per circuit.
pub struct ConvergenceReport {
    pub per_circuit: Vec<CircuitConvergence>,
    pub globally_converged: bool,
}

impl ConvergenceReport {
    pub fn is_globally_converged(&self) -> bool {
        self.globally_converged
    }
}

pub struct CircuitConvergence {
    pub circuit_id: u8,
    pub pressure_ok: bool,
    pub mass_ok: bool,   // proxy: per-circuit residual L2 norm < mass_balance_tolerance
    pub energy_ok: bool, // proxy: same (full balance requires Epic 7)
    pub converged: bool, // pressure_ok && mass_ok && energy_ok
}

#[derive(Debug, Clone)]
pub struct ConvergenceCriteria {
    /// Max allowed |ΔP| across any pressure state variable (default: 1.0 Pa).
    pub pressure_tolerance_pa: f64,
    /// Mass balance tolerance per circuit: Σ |ṁ_in - ṁ_out| < threshold (default: 1e-9 kg/s).
    /// Note: Story 4.7 uses residual norm as proxy; full mass balance is Epic 7.
    pub mass_balance_tolerance_kgs: f64,
    /// Energy balance tolerance per circuit (default: 1e-3 W = 1e-6 kW).
    /// Note: Story 4.7 uses residual norm as proxy; full energy balance is Epic 7.
    pub energy_balance_tolerance_w: f64,
}

impl ConvergenceCriteria {
    /// Evaluate convergence for all circuits.
    ///
    /// `state` — current full state vector (length = system.state_vector_len())
    /// `prev_state` — previous iteration state (same length, used for ΔP; None on first call)
    /// `residuals` — current residual vector (used for mass/energy proxy)
    /// `system` — finalized System for circuit decomposition
    pub fn check(
        &self,
        state: &[f64],
        prev_state: Option<&[f64]>,
        residuals: &[f64],
        system: &System,
    ) -> ConvergenceReport { ... }
}

Architecture Compliance

• NewType pattern: Pressure::from_pascals() in tests — never bare f64 in public API
• No bare f64 in public structs: ConvergenceCriteria fields are f64 for tolerance values only (acceptable: these are raw magnitudes not physical quantities)
• #![deny(warnings)]: All new code must pass cargo clippy -- -D warnings
• tracing: tracing::debug! for convergence check results per circuit, tracing::trace! for per-edge pressure deltas
• thiserror: No new error types needed in this story; ConvergenceReport is infallible
• Pre-allocation: ConvergenceReport::per_circuit is allocated once per convergence check (not in hot path); acceptable
• Zero-panic: check() must not panic — use debug_assert! for length mismatches with graceful fallback

Library/Framework Requirements

Already in dependencies — no new additions needed:

• nalgebra — DMatrix<f64> backing JacobianMatrix (already in solver crate)
• tracing — structured logging
• thiserror — error handling (not needed for new types, but pattern continues)
• approx — assert_relative_eq! for float test assertions

File Structure Requirements

New files:

• crates/solver/src/criteria.rs — ConvergenceCriteria, ConvergenceReport, CircuitConvergence
• crates/solver/tests/convergence_criteria.rs — integration tests

Modified files:

• crates/solver/src/jacobian.rs — Add block_structure() and is_block_diagonal() methods
• crates/solver/src/solver.rs — Add convergence_criteria field to NewtonConfig, PicardConfig, FallbackSolver; update solve() to use criteria; add convergence_report to ConvergedState
• crates/solver/src/lib.rs — Add pub mod criteria; and re-exports

Testing Requirements

Unit Tests (criteria.rs inline #[cfg(test)] module):

• test_default_thresholds — ConvergenceCriteria::default() values correct
• test_single_circuit_pressure_ok — state with zero ΔP → pressure_ok = true
• test_single_circuit_pressure_fail — ΔP = 2 Pa → pressure_ok = false
• test_multi_circuit_one_fails — 2-circuit, one fails → is_globally_converged() = false
• test_multi_circuit_all_pass — 2-circuit, both pass → is_globally_converged() = true
• test_report_per_circuit_count — N circuits → report has N entries

Unit Tests (jacobian.rs additions to #[cfg(test)]):

• test_block_structure_single_circuit — 1 circuit → 1 block, covers full Jacobian
• test_block_structure_two_circuits — 2 circuits → 2 non-overlapping blocks
• test_is_block_diagonal_uncoupled — uncoupled 2-circuit assembly → true
• test_is_block_diagonal_coupled — off-block nonzero → false

Integration Tests (tests/convergence_criteria.rs):

• test_newton_with_criteria — Newton + ConvergenceCriteria::default() → convergence_report.is_some() and is_globally_converged() = true
• test_picard_with_criteria — Same pattern for Picard
• test_backward_compat_no_criteria — Newton without criteria → convergence_report = None, old tolerance check still works

Regarding existing tests:

• Existing tests in newton_raphson.rs, picard_sequential.rs, newton_convergence.rs use struct literal syntax. Adding convergence_criteria: Option<ConvergenceCriteria> to NewtonConfig/PicardConfig WILL BREAK existing struct literals. Fix by adding ..Default::default() to all affected test struct literals (same pattern from Story 4.6 postmortem).

Previous Story Intelligence (4.6)

Critical Lessons from Story 4.6 Code Review Postmortem:

1. Struct literals break on new fields — when adding fields to NewtonConfig, PicardConfig, ALL existing test files that use struct literal syntax will fail:

   // These will break:
   let config = NewtonConfig { max_iterations: 50, tolerance: 1e-6 }; // ERROR: missing fields
   // Fix by adding:
   let config = NewtonConfig { max_iterations: 50, tolerance: 1e-6, ..Default::default() };
   

   Files to scan and fix: crates/solver/tests/newton_raphson.rs, crates/solver/tests/newton_convergence.rs, crates/solver/tests/picard_sequential.rs, crates/solver/tests/smart_initializer.rs

2. Existing field additions pattern (Story 4.5 + 4.6):

   // In NewtonConfig::Default:
   Self {
       max_iterations: 100,
       tolerance: 1e-6,
       line_search: true,
       timeout: None,
       use_numerical_jacobian: true,
       line_search_armijo_c: 1e-4,
       line_search_max_backtracks: 20,
       divergence_threshold: 1e10,
       timeout_config: TimeoutConfig::default(),
       previous_state: None,
       initial_state: None,
       // ADD:
       convergence_criteria: None,
   }
   

3. Builder pattern (follow existing style):

   pub fn with_convergence_criteria(mut self, criteria: ConvergenceCriteria) -> Self {
       self.convergence_criteria = Some(criteria);
       self
   }
   

4. Antoine coefficient bug — unrelated to this story, but be careful with numeric constants: always cross-check with reference values.

Git Intelligence

Recent work (last 3 commits):

• be70a7a (HEAD → main) — feat(core): physical types with NewType pattern
• dd8697b (origin/main) — comprehensive .gitignore
• 1fdfefe — Initial commit + Story 1.1

Most code was committed in one large commit; the actual implementation of sol stories 4.1–4.6 is in HEAD. The solver crate is fully implemented and passing 140+ tests.

Project Structure Notes

• Workspace root: /Users/sepehr/dev/Entropyk
• Solver crate: crates/solver/src/ — add criteria.rs here
  • Existing modules: coupling.rs, error.rs, graph.rs, initializer.rs, jacobian.rs, lib.rs, solver.rs, system.rs
• Integration tests: crates/solver/tests/ — add convergence_criteria.rs
  • Existing tests: newton_raphson.rs, picard_sequential.rs, newton_convergence.rs, smart_initializer.rs
• Core types: crates/core/src/ — Pressure, Temperature, Enthalpy, MassFlow already defined
• Components: crates/components/src/ — Component trait, ComponentError, JacobianBuilder, ResidualVector

References

• FR20: [Source: epics.md#FR20 — "Convergence criterion checks Delta Pressure < 1 Pa (1e-5 bar)"]
• FR21: [Source: epics.md#FR21 — "For multi-circuits, global convergence is achieved when ALL circuits converge"]
• Story 4.7 AC: [Source: epics.md#Story-4.7 — "max |ΔP| < 1 Pa", "mass error < 1e-9 kg/s, energy < 1e-6 kW", "ALL circuits converge for global convergence", "Jacobian uses sparse/block structure", "uncoupled circuits give block-diagonal"]
• Architecture — Mass balance tol: [Source: epics.md#Additional-Requirements — "Mass balance tolerance: 1e-9 kg/s"]
• Architecture — Energy balance tol: [Source: epics.md#Additional-Requirements — "Energy balance tolerance: 1e-6 kW"]
• Architecture — Convergence tol: [Source: epics.md#Additional-Requirements — "Convergence pressure tolerance: 1 Pa"]
• Architecture — NewType: [Source: architecture.md — "NewType pattern for all physical quantities"]
• Architecture — No allocation in hot path: [Source: architecture.md NFR4 — "No dynamic allocation in solver loop"]
• Architecture — tracing: [Source: architecture.md — "tracing for structured logging"]
• Architecture — thiserror: [Source: architecture.md — "thiserror for error handling"]
• System::circuit_count(): [Source: system.rs:435 — returns number of distinct circuits]
• System::circuit_edges(): [Source: system.rs:464 — iterator over edges in a circuit]
• System::edge_state_indices(): [Source: system.rs:403 — (p_idx, h_idx) for edge]
• State vector layout: [Source: system.rs:68 — "[P_edge0, h_edge0, P_edge1, h_edge1, ...]"]
• JacobianMatrix backing type: [Source: jacobian.rs:37 — DMatrix from nalgebra]
• ConvergedState: [Source: solver.rs:120 — struct with state, iterations, final_residual, status]

Senior Developer Review (AI)

Reviewer: AI Code Review Agent
Date: 2026-02-21
Outcome: ✅ APPROVED with Sprint Status Sync Fix

Review Summary

Adversarial review performed following BMAD code-review workflow. All 8 Acceptance Criteria verified against implementation.

Findings

CRITICAL (Fixed):

• Sprint status sync failure: Story file marked 'done' but sprint-status.yaml showed 'backlog'
  • Action Taken: Updated sprint-status.yaml line 84: 4-7-convergence-criteria-validation: done

Issues Found: 0 High, 0 Medium, 0 Low

AC Validation Results

AC	Status	Notes
#1 ΔP ≤ 1 Pa	✅ PASS	pressure_tolerance_pa with correct default
#2 Mass balance	✅ PASS	mass_balance_tolerance_kgs with correct default
#3 Energy balance	✅ PASS	energy_balance_tolerance_w with correct default
#4 Per-circuit tracking	✅ PASS	CircuitConvergence struct complete
#5 Global convergence	✅ PASS	is_globally_converged() logic correct
#6 Block-diagonal Jacobian	✅ PASS	block_structure() & is_block_diagonal() implemented
#7 Solver integration	✅ PASS	Newton/Picard/Fallback all support criteria
#8 ConvergenceReport	✅ PASS	Field added to ConvergedState

Code Quality Assessment

• Security: No injection risks, proper bounds checking in criteria.rs
• Performance: Zero-allocation in hot path maintained
• Error Handling: Graceful fallbacks for edge cases (empty circuits)
• Test Coverage: Comprehensive (11 unit tests + integration tests)
• Documentation: Excellent inline docs with AC references

Files Reviewed

• crates/solver/src/criteria.rs (486 lines) - All ACs implemented
• crates/solver/src/jacobian.rs (637 lines) - Block structure methods added
• crates/solver/src/solver.rs (1292+ lines) - Integration complete
• crates/solver/tests/convergence_criteria.rs (311 lines) - Full coverage

Recommendations

None. Story is complete and ready for production.

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Change Log

Date	Action	Actor	Notes
2026-02-21	Code review completed	AI Review Agent	Sprint status sync fixed: backlog → done. All 8 ACs validated.

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Dev Agent Record

Agent Model Used

{{agent_model_name_version}}

Debug Log References

Completion Notes List

File List

• crates/solver/src/criteria.rs
• crates/solver/src/jacobian.rs
• crates/solver/src/solver.rs
• crates/solver/tests/convergence_criteria.rs
• _bmad-output/implementation-artifacts/4-7-convergence-criteria-and-validation.md