fix: fix bugs and improve docs for prototracks-to-parameters algorithm (

#2567)

Self explaining.

Examples/Algorithms/TrackFindingExaTrkX/include/ActsExamples/TrackFindingExaTrkX/PrototracksToParameters.hpp

@@ -30,10 +30,16 @@ namespace ActsExamples {
 class PrototracksToParameters final : public IAlgorithm {
  public:
   struct Config {
+    /// The prototrack for that parameters should be computed
     std::string inputProtoTracks;
+    /// The spacepoint collection
     std::string inputSpacePoints;
+    /// The seeds created on-the-fly from which the parameters actually are
+    /// computed
     std::string outputSeeds = "seeds-from-prototracks";
+    /// The prototracks for which parameters where computed successfully
     std::string outputProtoTracks = "remaining-prototracks";
+    /// The output parameters
     std::string outputParameters = "parameters";
 
     /// Whether to make tight seeds (closest 3 hits to beampipe) or large

Examples/Algorithms/TrackFindingExaTrkX/src/PrototracksToParameters.cpp

@@ -41,6 +41,9 @@ PrototracksToParameters::PrototracksToParameters(Config cfg,
   if (m_cfg.geometry == nullptr) {
     throw std::invalid_argument("No geometry given");
   }
+  if (m_cfg.magneticField == nullptr) {
+    throw std::invalid_argument("No magnetic field given");
+  }
 
   // Set up the track parameters covariance (the same for all tracks)
   for (std::size_t i = Acts::eBoundLoc0; i < Acts::eBoundSize; ++i) {

Examples/Python/src/ExaTrkXTrackFinding.cpp

@@ -212,10 +212,10 @@ void addExaTrkXTrackFinding(Context &ctx) {
                  py::arg("timing") = nullptr);
   }
 
-  ACTS_PYTHON_DECLARE_ALGORITHM(ActsExamples::PrototracksToParameters, mex,
-                                "PrototracksToParameters", inputProtoTracks,
-                                inputSpacePoints, outputSeeds, outputParameters,
-                                outputProtoTracks, geometry, buildTightSeeds);
+  ACTS_PYTHON_DECLARE_ALGORITHM(
+      ActsExamples::PrototracksToParameters, mex, "PrototracksToParameters",
+      inputProtoTracks, inputSpacePoints, outputSeeds, outputParameters,
+      outputProtoTracks, geometry, magneticField, buildTightSeeds);
 
   ACTS_PYTHON_DECLARE_ALGORITHM(
       ActsExamples::TrackFindingFromPrototrackAlgorithm, mex,