Keep existing detector-order generation behavior

Author: arshpreetmaan

src/py/_tesseract_py_util/gari.py

@@ -715,7 +715,7 @@ def build_detector_orders(
     method: object | None = None,
     seed: int = 0,
 ) -> list[list[int]]:
-    """Builds orders for a source-aligned GARI DEM, with virtual IDs last."""
+    """Builds traversal orders for a source-aligned GARI DEM."""
     from tesseract_decoder import utils
 
     source_dem = _circuit_to_gari_source_dem(circuit)
@@ -727,11 +727,13 @@ def build_detector_orders(
     virtual_detectors = list(
         range(source_detector_count, gari_dem.num_detectors)
     )
+    source_positions = utils.build_det_orders(
+        source_dem, num_det_orders, method=method, seed=seed
+    )
     return [
-        order + virtual_detectors
-        for order in utils.build_det_orders(
-            source_dem, num_det_orders, method=method, seed=seed
-        )
+        sorted(range(source_detector_count), key=positions.__getitem__)
+        + virtual_detectors
+        for positions in source_positions
     ]
 
 

src/py/_tesseract_py_util/gari_test.py

@@ -170,7 +170,7 @@ def test_public_circuit_conversion_and_file_output(tmp_path):
     np.testing.assert_array_equal(
         checks.toarray(), transform.checks[[2, 0, 3, 1, 4, 5], :].toarray()
     )
-    source_orders = utils.build_det_orders(
+    source_positions = utils.build_det_orders(
         gari._circuit_to_gari_source_dem(circuit),
         2,
         method=utils.DetOrder.DetCoordinate,
@@ -182,7 +182,10 @@ def test_public_circuit_conversion_and_file_output(tmp_path):
         2,
         method=utils.DetOrder.DetCoordinate,
         seed=0,
-    ) == [order + [4, 5] for order in source_orders]
+    ) == [
+        sorted(range(4), key=positions.__getitem__) + [4, 5]
+        for positions in source_positions
+    ]
 
     block_dem = public_gari.circuit_to_gari(
         circuit,

src/py/utils_test.py

@@ -55,38 +55,21 @@ def test_build_det_orders_default_index():
 
 
 def test_build_det_orders_bfs():
-    path_dem = stim.DetectorErrorModel("""
-        error(0.1) D0 D1
-        error(0.1) D1 D2
-        error(0.1) D2 D3
-        error(0.1) D3 D4
-    """)
-    orders = tesseract_decoder.utils.build_det_orders(
-        path_dem,
-        num_det_orders=8,
+    assert tesseract_decoder.utils.build_det_orders(
+        _DETECTOR_ERROR_MODEL,
+        num_det_orders=1,
         method=tesseract_decoder.utils.DetOrder.DetBFS,
         seed=0,
-    )
-    for order in orders:
-        distances_from_start = [abs(detector - order[0]) for detector in order]
-        assert distances_from_start == sorted(distances_from_start)
+    ) == [[0, 1]]
 
 
 def test_build_det_orders_coordinate():
-    dem = stim.DetectorErrorModel("""
-        detector(0) D0
-        detector(3) D1
-        detector(1) D2
-        detector(4) D3
-        detector(2) D4
-    """)
-    order = tesseract_decoder.utils.build_det_orders(
-        dem,
+    assert tesseract_decoder.utils.build_det_orders(
+        _DETECTOR_ERROR_MODEL,
         num_det_orders=1,
         method=tesseract_decoder.utils.DetOrder.DetCoordinate,
         seed=0,
-    )[0]
-    assert order in ([3, 1, 4, 2, 0], [0, 2, 4, 1, 3])
+    ) == [[0, 1]]
 
 
 def test_build_det_orders_index():

src/utils.cc

@@ -23,7 +23,6 @@
 #include <queue>
 #include <random>
 #include <string>
-#include <utility>
 
 #include "common.h"
 #include "stim.h"
@@ -122,7 +121,11 @@ static std::vector<std::vector<size_t>> build_det_orders_bfs(const stim::Detecto
         } while (visited[start]);
       }
     }
-    det_orders[det_order] = std::move(perm);
+    std::vector<size_t> inv_perm(graph.size());
+    for (size_t i = 0; i < perm.size(); ++i) {
+      inv_perm[perm[i]] = i;
+    }
+    det_orders[det_order] = inv_perm;
   }
   return det_orders;
 }
@@ -156,7 +159,11 @@ static std::vector<std::vector<size_t>> build_det_orders_coordinate(
     std::sort(perm.begin(), perm.end(), [&](const size_t& i, const size_t& j) {
       return inner_products[i] > inner_products[j];
     });
-    det_orders[det_order] = std::move(perm);
+    std::vector<size_t> inv_perm(dem.count_detectors());
+    for (size_t i = 0; i < perm.size(); ++i) {
+      inv_perm[perm[i]] = i;
+    }
+    det_orders[det_order] = inv_perm;
   }
   return det_orders;
 }

src/utils.pybind.h

@@ -110,8 +110,8 @@ void add_utils_module(py::module& root) {
         Returns
         -------
         list[list[int]]
-            A list of detector orderings. Each inner list gives the detector
-            IDs in traversal order.
+            A list of detector orderings. Each inner list maps a detector index
+            to its position in the ordering.
     )pbdoc");
   m.def(
       "get_errors_from_dem",