Fix #295: Add DirectedTwoCommodityIntegralFlow model by GiggleLiu · Pull Request #660 · CodingThrust/problem-reductions

GiggleLiu · 2026-03-16T09:11:48Z

Summary

Add the Directed Two-Commodity Integral Flow problem model (Garey & Johnson A2 ND38) -- a satisfaction problem asking whether two integral flow functions can simultaneously satisfy joint arc capacity, flow conservation, and requirement constraints on a directed graph.

Fixes #295

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

codecov · 2026-03-16T09:13:25Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.00%. Comparing base (a4c3516) to head (2dfd9a2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #660      +/-   ##
==========================================
+ Coverage   96.97%   97.00%   +0.02%     
==========================================
  Files         277      279       +2     
  Lines       37161    37433     +272     
==========================================
+ Hits        36038    36311     +273     
+ Misses       1123     1122       -1

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Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

GiggleLiu · 2026-03-16T10:31:04Z

Implementation Summary

Changes

src/models/graph/directed_two_commodity_integral_flow.rs — New satisfaction problem model: struct with 8 fields (graph, capacities, 4 terminals, 2 requirements), Problem impl with Metric = bool, SatisfactionProblem marker, declare_variants! with complexity (max_capacity + 1)^(2 * num_arcs), ProblemSchemaEntry registration, canonical model example
src/unit_tests/models/graph/directed_two_commodity_integral_flow.rs — 12 unit tests: creation, evaluation (satisfying/unsatisfying), capacity violation, conservation violation, solver YES/NO, serialization, paper example, higher capacity, accessors, problem name
src/models/graph/mod.rs — Module registration + canonical_model_example_specs
src/models/mod.rs — Re-export DirectedTwoCommodityIntegralFlow
src/lib.rs — Added to prelude
src/unit_tests/trait_consistency.rs — Added check_problem_trait entry
problemreductions-cli/src/cli.rs — 7 new CLI flags (capacities, source_1, sink_1, source_2, sink_2, requirement_1, requirement_2) + help table entry
problemreductions-cli/src/commands/create.rs — Match arm for pred create DirectedTwoCommodityIntegralFlow with usage hint + all_data_flags_empty update
docs/paper/reductions.typ — Display name + problem-def with formal definition, background, example with CeTZ directed graph diagram
docs/paper/references.bib — Added Even, Itai, Shamir (1976) reference
src/example_db/fixtures/examples.json — Regenerated (33 model examples)
docs/src/reductions/problem_schemas.json — Regenerated (42 schemas)
docs/src/reductions/reduction_graph.json — Regenerated

Deviations from Plan

Simplified flow conservation logic: removed redundant second conservation check. The problem definition exempts all four terminals from conservation for both commodities, so a single loop with a terminals.contains(&v) check suffices.

Open Questions

None

Copilot

Pull request overview

Adds a new NP-complete graph satisfaction model, DirectedTwoCommodityIntegralFlow (G&J A2 ND38), and wires it into exports, CLI instance creation, examples, and documentation generation artifacts.

Changes:

Introduces DirectedTwoCommodityIntegralFlow model with feasibility evaluation, schema registration, variant declaration, and example-db fixture.
Adds unit tests covering creation, evaluation (yes/no), brute-force solving, and serialization.
Integrates the model into the CLI (pred create), library re-exports/prelude, and generated docs JSON / paper definition.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/models/graph/directed_two_commodity_integral_flow.rs	New model implementation, schema registration, variant declaration, and example-db spec
src/models/graph/mod.rs	Registers the new graph model module, re-export, and example spec wiring
src/models/mod.rs	Re-exports the new model from the top-level `models` module
src/lib.rs	Adds the model to the public prelude exports
src/unit_tests/models/graph/directed_two_commodity_integral_flow.rs	New model unit tests (feasibility, solver behavior, serde)
src/unit_tests/trait_consistency.rs	Adds trait consistency coverage for the new problem type
problemreductions-cli/src/cli.rs	Adds CLI flags documentation and new CreateArgs fields for the model
problemreductions-cli/src/commands/create.rs	Adds `pred create DirectedTwoCommodityIntegralFlow` construction + example string
src/example_db/fixtures/examples.json	Adds an example-db fixture instance and solutions for the model
docs/src/reductions/problem_schemas.json	Adds generated schema entry for the new model
docs/src/reductions/reduction_graph.json	Adds generated reduction graph node entry (and index shifts)
docs/paper/reductions.typ	Adds paper definition + illustrative figure for the new model
docs/paper/references.bib	Adds Even–Itai–Shamir (1976) reference

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src/models/graph/directed_two_commodity_integral_flow.rs

+                    net_flow_in -= config[offset + a] as i64;
+                }
+            }
+            if (net_flow_in as u64) < req {


src/models/graph/directed_two_commodity_integral_flow.rs

+    ProblemSchemaEntry {
+        name: "DirectedTwoCommodityIntegralFlow",
+        display_name: "Directed Two-Commodity Integral Flow",
+        aliases: &[],


src/models/graph/directed_two_commodity_integral_flow.rs

+            for v in 0..n {
+                if terminals.contains(&v) {
+                    continue;
+                }
+                let mut flow_in: i64 = 0;
+                let mut flow_out: i64 = 0;
+                for (a, &(u, w)) in arcs.iter().enumerate() {
+                    if w == v {
+                        flow_in += config[offset + a] as i64;
+                    }
+                    if u == v {
+                        flow_out += config[offset + a] as i64;
+                    }
+                }
+                if flow_in != flow_out {


GiggleLiu · 2026-03-16T13:12:23Z

Review Pipeline Report

Check	Result
Copilot comments	3 fixed
Issue/human comments	4 checked, 3 fixed
Structural review	18/18 passed
CI	green
Agentic test	passed
Needs human decision	none
Board	Review pool -> Under review -> Final review

Remaining issues for final review

None.

Generated by review-pipeline.

GiggleLiu · 2026-03-16T13:19:03Z

Review Pipeline Report

Check	Result
Copilot comments	3 fixed
Issue/human comments	4 checked, 3 fixed
Structural review	18/18 passed
CI	green
Agentic test	passed after follow-up fixes
Needs human decision	none
Board	Review pool -> Under review -> Final review

Remaining issues for final review

None.

Final follow-up fixes after the first pass:

added a brute-force hint to the default pred solve error for DirectedTwoCommodityIntegralFlow
added D2CIF examples and config-ordering guidance to README.md and docs/src/cli.md
corrected the make cli installation wording in the docs

Generated by review-pipeline.

Merge main into branch, resolving conflicts to include both DirectedTwoCommodityIntegralFlow and main's new models (SteinerTree, SetBasis, LengthBoundedDisjointPaths, UndirectedTwoCommodityIntegralFlow). Regenerated JSON fixtures. Added test for wrong-length config to cover the early return in is_feasible(). Reverted README.md to main. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

… requirements) Both DirectedTwoCommodityIntegralFlow and UndirectedTwoCommodityIntegralFlow share the same CLI fields. The merge with main created duplicates. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

zazabap · 2026-03-16T14:41:46Z

Final Review — Approved

Aspect	Result
Comments	All addressed (3 Copilot fixes by review pipeline, 1 coverage test added)
Usefulness	Useful — GJ ND38, cornerstone of integral multicommodity flow NP-completeness
Safety	Safe (README reverted, no unrelated changes)
Completeness	Complete (18/18 structural checks, paper entry, CLI tests, trait consistency)
Quality	82% — clean implementation, CI all green, proper references

Fixes applied during final review:

Resolved merge conflicts with main (SteinerTree, SetBasis, LengthBoundedDisjointPaths, UndirectedTwoCommodityIntegralFlow)
Added coverage test for wrong-config-length early return
Reverted unrelated README.md changes
Removed duplicate CLI fields from merge (shared with UndirectedTwoCommodityIntegralFlow)

zazabap

Final review passed — all CI green, quality 82%.

zazabap

Final review passed.

Add plan for #295: DirectedTwoCommodityIntegralFlow

7e094ab

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

GiggleLiu and others added 2 commits March 16, 2026 18:27

Implement #295: Add DirectedTwoCommodityIntegralFlow model

0d24385

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

chore: remove plan file after implementation

f9da9d9

GiggleLiu requested a review from Copilot March 16, 2026 10:35

Copilot started reviewing on behalf of GiggleLiu March 16, 2026 10:36 View session

Copilot AI reviewed Mar 16, 2026

View reviewed changes

fix: address PR #660 review follow-ups

a898594

fix: improve D2CIF CLI guidance

900b87a

zazabap and others added 2 commits March 16, 2026 14:31

zazabap self-requested a review March 16, 2026 14:40

zazabap approved these changes Mar 16, 2026

View reviewed changes

zazabap merged commit 47ea067 into main Mar 16, 2026
3 checks passed

zazabap approved these changes Mar 16, 2026

View reviewed changes

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Fix #295: Add DirectedTwoCommodityIntegralFlow model#660

Fix #295: Add DirectedTwoCommodityIntegralFlow model#660
zazabap merged 7 commits intomainfrom
issue-295-directed-two-commodity-integral-flow

GiggleLiu commented Mar 16, 2026

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GiggleLiu commented Mar 16, 2026

Summary

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GiggleLiu commented Mar 16, 2026

Implementation Summary

Changes

Deviations from Plan

Open Questions

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Pull request overview

Reviewed changes

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GiggleLiu commented Mar 16, 2026

Review Pipeline Report

Remaining issues for final review

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GiggleLiu commented Mar 16, 2026

Review Pipeline Report

Remaining issues for final review

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zazabap commented Mar 16, 2026

Final Review — Approved

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codecov bot commented Mar 16, 2026 •

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