Made D_sparse no longer optional, and fixed surface_code segfault

Signed-off-by: Chuck Ketcham <[email protected]>

Author: cketcham2333

libs/qec/include/cudaq/qec/realtime/decoding_config.h

@@ -120,7 +120,7 @@ struct decoder_config {
   uint64_t syndrome_size = 0;
   std::vector<std::int64_t> H_sparse;
   std::vector<std::int64_t> O_sparse;
-  std::optional<std::vector<std::int64_t>> D_sparse;
+  std::vector<std::int64_t> D_sparse;
   std::variant<single_error_lut_config, multi_error_lut_config,
                nv_qldpc_decoder_config, sliding_window_config>
       decoder_custom_args;

libs/qec/lib/realtime/config.cpp

@@ -351,7 +351,7 @@ struct MappingTraits<cudaq::qec::decoding::config::decoder_config> {
     io.mapRequired("syndrome_size", config.syndrome_size);
     io.mapRequired("H_sparse", config.H_sparse);
     io.mapRequired("O_sparse", config.O_sparse);
-    io.mapOptional("D_sparse", config.D_sparse);
+    io.mapRequired("D_sparse", config.D_sparse);
 
     // Validate that the number of rows in the H_sparse vector is equal to
     // syndrome_size.
@@ -383,9 +383,9 @@ struct MappingTraits<cudaq::qec::decoding::config::decoder_config> {
     // Validate that if the D_sparse is provided, it is a valid D matrix. That
     // means that the number of rows in the D_sparse matrix should be equal to
     // the number of rows in the H_sparse matrix, and no row should be empty.
-    if (config.D_sparse.has_value()) {
+    if (!config.D_sparse.empty()) {
       auto num_D_rows =
-          std::count(config.D_sparse->begin(), config.D_sparse->end(), -1);
+          std::count(config.D_sparse.begin(), config.D_sparse.end(), -1);
       if (num_D_rows != config.syndrome_size) {
         throw std::runtime_error("Number of rows in D_sparse vector is not "
                                  "equal to syndrome_size: " +
@@ -394,14 +394,13 @@ struct MappingTraits<cudaq::qec::decoding::config::decoder_config> {
       }
       // No row should be empty, which means that there should be no
       // back-to-back -1 values.
-      for (std::size_t i = 0; i < config.D_sparse->size() - 1; ++i) {
-        if (config.D_sparse->at(i) == -1 && config.D_sparse->at(i + 1) == -1) {
+      for (std::size_t i = 0; i < config.D_sparse.size() - 1; ++i) {
+        if (config.D_sparse.at(i) == -1 && config.D_sparse.at(i + 1) == -1) {
           throw std::runtime_error("D_sparse row is empty for decoder " +
                                    std::to_string(config.id));
         }
       }
     }
-
 #define INIT_AND_MAP_DECODER_CUSTOM_ARGS(type)                                 \
   do {                                                                         \
     if (!std::holds_alternative<type>(config.decoder_custom_args)) {           \

libs/qec/lib/realtime/realtime_decoding.cpp

@@ -73,8 +73,8 @@ int configure_decoders(
       auto observable_matrix = cudaq::qec::pcm_from_sparse_vec(
           decoder_config.O_sparse, num_observables, decoder_config.block_size);
       new_decoder->set_O_sparse(decoder_config.O_sparse);
-      if (decoder_config.D_sparse.has_value()) {
-        new_decoder->set_D_sparse(*decoder_config.D_sparse);
+      if (!decoder_config.D_sparse.empty()) {
+        new_decoder->set_D_sparse(decoder_config.D_sparse);
       } else {
         throw std::runtime_error(
             "D_sparse must be provided in decoder configuration");

libs/qec/unittests/realtime/app_examples/surface_code-1.cpp

@@ -47,12 +47,9 @@ void save_dem_to_file(const cudaq::qec::detector_error_model &dem,
         cudaq::qec::pcm_to_sparse_vec(dem.observables_flips_matrix);
     config.D_sparse = cudaq::qec::generate_timelike_sparse_detector_matrix(
         numSyndromesPerRound, numRounds, /*include_first_round=*/false);
-    config.decoder_custom_args =
-        cudaq::qec::decoding::config::multi_error_lut_config();
-    auto &multi_error_lut_config =
-        std::get<cudaq::qec::decoding::config::multi_error_lut_config>(
-            config.decoder_custom_args);
-    multi_error_lut_config.lut_error_depth = 2;
+    cudaq::qec::decoding::config::multi_error_lut_config lut_config;
+    lut_config.lut_error_depth = 2;
+    config.decoder_custom_args = lut_config;
     multi_config.decoders.push_back(config);
   }
   std::string config_str = multi_config.to_yaml_str(200);