Change simplex to re-use DEM preprocessing logic from utils, to fix bug with logical_observable instruction (#193)

These instructions rarely appear in valid in DEMs but are allowed and
previously caused an error.
Fixes #190

Author: noajshu

AGENTS.md

@@ -18,8 +18,7 @@ bazel build src:tesseract src:simplex
 ## Running Tests with Bazel
 
 ```bash
-bazel test src:all
-bazel test //src/py:all
+bazel test src/...
 ```
 
 ## Building with CMake

src/simplex.cc

@@ -18,6 +18,7 @@
 
 #include "Highs.h"
 #include "io/HMPSIO.h"
+#include "utils.h"
 
 constexpr size_t T_COORD = 2;
 
@@ -51,24 +52,13 @@ SimplexDecoder::SimplexDecoder(SimplexConfig _config) : config(_config) {
   dem_error_to_error = std::move(dem_error_map);
   error_to_dem_error = common::invert_error_map(dem_error_to_error, config.dem.count_errors());
 
-  std::vector<double> detector_t_coords(config.dem.count_detectors());
-  for (const stim::DemInstruction& instruction : config.dem.flattened().instructions) {
-    switch (instruction.type) {
-      case stim::DemInstructionType::DEM_SHIFT_DETECTORS:
-        throw std::runtime_error("DEM_SHIFT_DETECTORS instruction is not supported.");
-        break;
-      case stim::DemInstructionType::DEM_ERROR: {
-        if (!(instruction.arg_data[0] > 0)) {
-          throw std::invalid_argument("Error instruction probability must be greater than zero.");
-        }
-        errors.emplace_back(instruction);
-        break;
-      }
-      case stim::DemInstructionType::DEM_DETECTOR:
-        detector_t_coords[instruction.target_data[0].val()] = instruction.arg_data[T_COORD];
-        break;
-      default:
-        throw std::runtime_error("Unsupported instruction type encountered.");
+  errors = get_errors_from_dem(config.dem.flattened());
+
+  std::vector<double> detector_t_coords(config.dem.count_detectors(), 0);
+  std::vector<std::vector<double>> detector_coords = get_detector_coords(config.dem);
+  for (size_t d = 0; d < detector_coords.size(); ++d) {
+    if (detector_coords[d].size() > T_COORD) {
+      detector_t_coords[d] = detector_coords[d][T_COORD];
     }
   }
   std::map<double, std::vector<size_t>> start_time_to_errors_map, end_time_to_errors_map;

src/tesseract.test.cc

@@ -219,6 +219,30 @@ TEST(tesseract, DecodersStripZeroProbabilityErrors) {
   EXPECT_EQ(s_dec.errors.size(), 2);
 }
 
+TEST(tesseract, GetDetectorCoordsAllowsLogicalObservableInstructionsInDem) {
+  stim::DetectorErrorModel dem(R"DEM(
+        error(0.1) D0 L0
+        detector(1,2,3) D0
+        logical_observable L0
+      )DEM");
+
+  std::vector<std::vector<double>> detector_coords = get_detector_coords(dem);
+  ASSERT_EQ(detector_coords.size(), 1);
+  ASSERT_EQ(detector_coords[0].size(), 3);
+  EXPECT_EQ(detector_coords[0][0], 1);
+  EXPECT_EQ(detector_coords[0][1], 2);
+  EXPECT_EQ(detector_coords[0][2], 3);
+}
+TEST(tesseract, SimplexAllowsLogicalObservableInstructionsInDem) {
+  stim::DetectorErrorModel dem(R"DEM(
+        error(0.1) D0 L0
+        detector(0,0,0) D0
+        logical_observable L0
+      )DEM");
+
+  EXPECT_NO_THROW({ SimplexDecoder s_dec(SimplexConfig{dem}); });
+}
+
 TEST(tesseract, DecoderErrorIndexMapsAreInOriginalDemCoordinates) {
   stim::DetectorErrorModel dem(R"DEM(
         error(0.1) D0
@@ -344,4 +368,4 @@ TEST(tesseract, EneighborsCorrectness_ComplexGrid) {
   EXPECT_EQ(t_dec.get_eneighbors()[5], expected_e5_neighbors);
   EXPECT_EQ(t_dec.get_eneighbors()[6], expected_e6_neighbors);
   EXPECT_EQ(t_dec.get_eneighbors()[7], expected_e7_neighbors);
-}
+}

src/utils.cc

@@ -45,6 +45,8 @@ std::vector<std::vector<double>> get_detector_coords(const stim::DetectorErrorMo
         detector_coords.push_back(coord);
         break;
       }
+      case stim::DemInstructionType::DEM_LOGICAL_OBSERVABLE:
+        break;
       default:
         throw std::invalid_argument(
             "Unexpected DemInstructionType found in the detector error model.");