mwpm_2d stub

Cargo.toml

@@ -24,6 +24,7 @@ pyo3 = "0.23"
 rand = "0.8"
 rand_chacha = "0.3"
 rand_xoshiro = "0.6"
+petgraph = "0.7"
 
 pecos-core = { version = "0.1.1", path = "crates/pecos-core" }
 pecos-qsim = { version = "0.1.1", path = "crates/pecos-qsim" }

crates/pecos-core/src/lib.rs

@@ -10,9 +10,12 @@
 // or implied. See the License for the specific language governing permissions and limitations under
 // the License.
 
+pub mod qubit_id;
 mod sets;
 mod sims_rngs;
+mod stabilizer_code;
 
+pub use qubit_id::QubitId;
 pub use sets::element::{Element, IndexableElement};
 pub use sets::set::Set;
 pub use sets::vec_set::VecSet;

crates/pecos-core/src/qubit_id.rs

@@ -0,0 +1,14 @@
+// Copyright 2025 The PECOS Developers
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+// in compliance with the License.You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software distributed under the License
+// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+// or implied. See the License for the specific language governing permissions and limitations under
+// the License.
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct QubitId(pub usize);

crates/pecos-core/src/stabilizer_code.rs

@@ -0,0 +1,13 @@
+use crate::qubit_id::QubitId;
+
+pub trait StabilizerCode {
+    fn num_data_qubits(&self) -> usize;
+
+    // Get a vector of the stabilizer generators used for the code.
+    // Todo: Utilize PauliSet when available
+    fn get_stabilizer_gens(&self) -> Vec<Vec<(usize, QubitId)>>;
+
+    // Get the boundaries of the code
+    // TODO: Consider adding identifiers to identify the boundary types
+    fn get_boundaries(&self) -> Vec<Vec<QubitId>>;
+}

crates/pecos-qec/Cargo.toml

@@ -11,8 +11,8 @@ categories.workspace = true
 description = "QEC for Rust PECOS."
 
 [dependencies]
-pecos-qsim = { workspace = true }
-pecos-decoders = { workspace = true}
+petgraph = { workspace = true }
+pecos-core = { workspace = true }
 
 [lints]
 workspace = true

crates/pecos-qec/src/decoders.rs

@@ -0,0 +1 @@
+pub mod mwpm_2d;

crates/pecos-qec/src/decoders/mwpm_2d.rs

@@ -0,0 +1,62 @@
+use pecos_core::QubitId;
+use petgraph::graph::NodeIndex;
+use petgraph::Graph;
+use std::collections::HashMap;
+
+// Recreate pecos/decoders/mwpm2d/{mwpm2d/py, precomputing.py}
+
+#[derive(Debug)]
+pub struct PrecomputedData {
+    x_graph: Graph<(), f64>,
+    z_graph: Graph<(), f64>,
+    virtual_edges: HashMap<NodeIndex, VirtualEdgeData>,
+    edge_to_data: HashMap<(NodeIndex, NodeIndex), QubitId>,
+}
+
+#[derive(Debug)]
+pub struct VirtualEdgeData {
+    pub virtual_node: NodeIndex,
+    pub weight: f64,
+    pub syndrome_path: Vec<NodeIndex>,
+    pub data_path: Vec<QubitId>,
+}
+
+struct Syndrome {}
+struct Recovery {}
+struct SurfaceCode {}
+
+// #[derive(Debug)]
+pub struct MWPM2DDecoder {
+    precomputed: PrecomputedData,
+    cached_recoveries: HashMap<Vec<Syndrome>, Recovery>,
+}
+
+impl MWPM2DDecoder {
+    pub fn new(code: &SurfaceCode) -> Self {
+        let precomputed = Self::precompute(code);
+        Self {
+            precomputed,
+            cached_recoveries: HashMap::new(),
+        }
+    }
+
+    fn precompute(code: &SurfaceCode) -> PrecomputedData {
+        // Build distance graphs and lookup tables
+        // Similar to precomputing.py
+        PrecomputedData {
+            x_graph: Graph::new(),
+            z_graph: Graph::new(),
+            virtual_edges: HashMap::new(),
+            edge_to_data: HashMap::new(),
+        }
+    }
+
+    pub fn decode(&mut self, syndromes: &[Syndrome]) -> Recovery {
+        // 1. Check cache
+        // 2. Build matching graph
+        // 3. Add virtual nodes
+        // 4. Find maximum weight perfect matching
+        // 5. Convert matching to recovery operations
+        Recovery {}
+    }
+}

crates/pecos-qec/src/lib.rs

@@ -11,3 +11,5 @@
 // the License.
 
 // pecos-qec stub. Left intentionally blank for now.
+
+mod decoders;