🚧 Add special_edges

Author: EarlMilktea

python/swiflow/common.py

@@ -79,6 +79,7 @@ def _special_edges(
     pplanes: Mapping[_V, PPlane] | None,
 ) -> set[tuple[_V, _V]]:
     """Compute special edges that can bypass partial order constraints in Pauli flow."""
+    # MEMO: Unify with Rust implementation
     ret: set[tuple[_V, _V]] = set()
     if pplanes is None:
         return ret

src/pflow.rs

@@ -1,7 +1,7 @@
 //! Maximally-delayed Pauli flow algorithm.
 
 use core::iter;
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 
 use fixedbitset::FixedBitSet;
 use pyo3::prelude::*;
@@ -434,6 +434,31 @@ pub fn find(g: Graph, iset: Nodes, oset: Nodes, pplanes: PPlanes) -> Option<(PFl
     }
 }
 
+/// Compute special edges that can bypass partial order constraints in Pauli flow.
+fn special_edges(g: &[Nodes], pflow: &PFlow, pplanes: &PPlanes) -> HashSet<(Node, Node)> {
+    let mut ret = HashSet::new();
+    for (&i, fi) in pflow {
+        for &j in fi.iter().filter(|&&j| i != j) {
+            if let Some(PPlane::X) = pplanes.get(&i) {
+                ret.insert((i, j));
+            }
+        }
+        let mut odd_fi = utils::odd_neighbors(g, fi);
+        odd_fi.remove(&i);
+        for &j in &odd_fi {
+            if let Some(PPlane::Z) = pplanes.get(&i) {
+                ret.insert((i, j));
+            }
+        }
+        for &j in fi.intersection(&odd_fi) {
+            if let Some(PPlane::Y) = pplanes.get(&i) {
+                ret.insert((i, j));
+            }
+        }
+    }
+    ret
+}
+
 /// Validates Pauli flow.
 ///
 /// # Errors
@@ -453,9 +478,11 @@ pub fn verify(
     let (f, layers) = pflow;
     let n = g.len();
     let vset = (0..n).collect::<Nodes>();
+    let special = special_edges(&g, &f, &pplanes);
     let f_flatiter = f
         .iter()
-        .flat_map(|(i, fi)| Iterator::zip(iter::repeat(i), fi.iter()));
+        .flat_map(|(i, fi)| Iterator::zip(iter::repeat(i), fi.iter()))
+        .filter(|&(&i, &j)| !special.contains(&(i, j)));
     common::check_domain(f_flatiter, &vset, &iset, &oset)?;
     check_def_geom(&f, &g, &pplanes)?;
     check_def_layer(&f, &layers, &g, &pplanes)?;