Add ILP solver backends (HiGHS, CPLEX, lp-solvers) and fix good_lp compatibility (#792)

* refactor: upgrade good_lp to 1.15.0 and add lp-solvers backend (#787)

- Upgrade good_lp from 1.14.2 to 1.15.0
- Add ilp-lp-solvers feature for Gurobi/CPLEX/CBC/GLPK support
  (via lp-solvers crate, which shells out to solver CLIs)
- Remove unused backend features (coin-cbc, clarabel, scip, lpsolve, microlp)
- Update CLI help text

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

* test: add prism graph HC→QAP→ILP roundtrip test (#780)

Verifies the full reduction chain HamiltonianCircuit → QuadraticAssignment
→ ILP on the prism graph (6 vertices, 9 edges) — the instance that
triggered #780. Confirms the extracted solution is a valid HC.

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

* refactor: replace lp-solvers with cplex backend

CPLEX is supported natively by good_lp via cplex-rs (direct C API),
no need for the lp-solvers shell-out approach.

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

* test: remove prism graph roundtrip test

Temporary test to verify #780 fix — no longer needed.

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

* feat: add lpsolve backend

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

* feat: add all good_lp solver backends

Add coin-cbc, clarabel, scip, microlp, and lp-solvers (Gurobi/GLPK via CLI).

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

* chore: keep only useful ILP backends (HiGHS, CPLEX, lp-solvers)

Remove coin-cbc, clarabel, scip, microlp, lpsolve — either inferior
to HiGHS or niche. lp-solvers covers Gurobi/GLPK via CLI shell-out.

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

* test: add prism graph HC→QAP→ILP roundtrip test

Restores the prism graph (6 vertices, 9 edges) end-to-end test
that exercises the HC → QAP → ILP → solve → extract pipeline.

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

* fix: downgrade good_lp to 1.14.2 to fix lp-solvers build on Rust 1.90

good_lp 1.15.0 uses `gen` as a variable name, which is a reserved
keyword in newer Rust compilers, breaking the lp-solvers feature.

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

---------

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

Author: isPANN

Cargo.toml

@@ -17,11 +17,8 @@ example-db = []
 ilp = ["ilp-highs"]  # backward compat shorthand
 ilp-solver = []      # marker: enables ILP solver code
 ilp-highs = ["ilp-solver", "dep:good_lp", "good_lp/highs"]
-ilp-coin-cbc = ["ilp-solver", "dep:good_lp", "good_lp/coin_cbc"]
-ilp-clarabel = ["ilp-solver", "dep:good_lp", "good_lp/clarabel"]
-ilp-scip = ["ilp-solver", "dep:good_lp", "good_lp/scip"]
-ilp-lpsolve = ["ilp-solver", "dep:good_lp", "good_lp/lpsolve"]
-ilp-microlp = ["ilp-solver", "dep:good_lp", "good_lp/microlp"]
+ilp-cplex = ["ilp-solver", "dep:good_lp", "good_lp/cplex-rs"]
+ilp-lp-solvers = ["ilp-solver", "dep:good_lp", "good_lp/lp-solvers"]
 
 [dependencies]
 petgraph = { version = "0.8", features = ["serde-1"] }

problemreductions-cli/Cargo.toml

@@ -19,11 +19,8 @@ default = ["highs"]
 all = ["highs", "mcp"]
 highs = ["problemreductions/ilp-highs"]
 mcp = ["dep:rmcp", "dep:tokio", "dep:schemars", "dep:tracing", "dep:tracing-subscriber"]
-coin-cbc = ["problemreductions/ilp-coin-cbc"]
-clarabel = ["problemreductions/ilp-clarabel"]
-scip = ["problemreductions/ilp-scip"]
-lpsolve = ["problemreductions/ilp-lpsolve"]
-microlp = ["problemreductions/ilp-microlp"]
+cplex = ["problemreductions/ilp-cplex"]
+lp-solvers = ["problemreductions/ilp-lp-solvers"]
 
 [dependencies]
 problemreductions = { version = "0.4.0", path = "..", default-features = false, features = ["example-db"] }

problemreductions-cli/src/cli.rs

@@ -767,10 +767,9 @@ Customized solver: exact witness recovery for select problems via structure-expl
 backends. Currently supports MinimumCardinalityKey, AdditionalKey, PrimeAttributeName,
 BoyceCoddNormalFormViolation, PartialFeedbackEdgeSet, and RootedTreeArrangement.
 
-ILP backend (default: HiGHS). To use a different backend:
-  cargo install problemreductions-cli --features coin-cbc
-  cargo install problemreductions-cli --features scip
-  cargo install problemreductions-cli --no-default-features --features clarabel")]
+ILP backend (default: HiGHS). To use CPLEX instead:
+  cargo install problemreductions-cli --features cplex
+(Requires CPLEX to be installed on your system.)")]
 pub struct SolveArgs {
     /// Problem JSON file (from `pred create`) or reduction bundle (from `pred reduce`). Use - for stdin.
     pub input: PathBuf,

src/unit_tests/rules/hamiltoniancircuit_quadraticassignment.rs

@@ -110,3 +110,39 @@ fn test_hamiltoniancircuit_to_quadraticassignment_extract_solution() {
         "extracted solution should be a valid HC"
     );
 }
+
+#[cfg(feature = "ilp-solver")]
+#[test]
+fn test_prism_graph_hc_via_qap_ilp_roundtrip() {
+    use crate::models::algebraic::ILP;
+    use crate::solvers::ILPSolver;
+
+    // Prism graph: 6 vertices, 9 edges — the instance from #780.
+    let edges = vec![
+        (0, 1),
+        (1, 2),
+        (2, 0),
+        (3, 4),
+        (4, 5),
+        (5, 3),
+        (0, 3),
+        (1, 4),
+        (2, 5),
+    ];
+    let hc = HamiltonianCircuit::new(SimpleGraph::new(6, edges));
+
+    // HC → QAP → ILP → solve → extract back
+    let r1 = ReduceTo::<QuadraticAssignment>::reduce_to(&hc);
+    let r2 = ReduceTo::<ILP<bool>>::reduce_to(r1.target_problem());
+    let ilp_sol = ILPSolver::new()
+        .solve(r2.target_problem())
+        .expect("ILP should be feasible");
+    let qap_sol = r2.extract_solution(&ilp_sol);
+    let hc_sol = r1.extract_solution(&qap_sol);
+
+    assert!(
+        hc.evaluate(&hc_sol).0,
+        "prism graph HC via QAP→ILP should produce a valid Hamiltonian circuit, got {:?}",
+        hc_sol
+    );
+}