CACell.h

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#ifndef RecoPixelVertexing_PixelTriplets_src_CACell_h
#define RecoPixelVertexing_PixelTriplets_src_CACell_h

#include <array>
#include <cmath>

#include "DataFormats/Math/interface/deltaPhi.h"
#include "RecoTracker/TkHitPairs/interface/RecHitsSortedInPhi.h"
#include "RecoTracker/TkTrackingRegions/interface/TrackingRegion.h"
#include "TrackingTools/TransientTrackingRecHit/interface/SeedingLayerSetsHits.h"

class CACellStatus {
public:
  unsigned char getCAState() const { return theCAState; }

  // if there is at least one left neighbor with the same state (friend), the state has to be increased by 1.
  void updateState() { theCAState += hasSameStateNeighbors; }

  bool isRootCell(const unsigned int minimumCAState) const { return (theCAState >= minimumCAState); }

public:
  unsigned char theCAState = 0;
  unsigned char hasSameStateNeighbors = 0;
};

class CACell {
public:
  using Hit = RecHitsSortedInPhi::Hit;
  using CAntuple = std::vector<unsigned int>;
  using CAntuplet = std::vector<unsigned int>;
  using CAColl = std::vector<CACell>;
  using CAStatusColl = std::vector<CACellStatus>;

  CACell(const HitDoublets* doublets, int doubletId, const int innerHitId, const int outerHitId)
      : theDoublets(doublets),
        theDoubletId(doubletId),
        theInnerR(doublets->rv(doubletId, HitDoublets::inner)),
        theInnerZ(doublets->z(doubletId, HitDoublets::inner)) {}

  Hit const& getInnerHit() const { return theDoublets->hit(theDoubletId, HitDoublets::inner); }

  Hit const& getOuterHit() const { return theDoublets->hit(theDoubletId, HitDoublets::outer); }

  float getInnerX() const { return theDoublets->x(theDoubletId, HitDoublets::inner); }

  float getOuterX() const { return theDoublets->x(theDoubletId, HitDoublets::outer); }

  float getInnerY() const { return theDoublets->y(theDoubletId, HitDoublets::inner); }

  float getOuterY() const { return theDoublets->y(theDoubletId, HitDoublets::outer); }

  float getInnerZ() const { return theInnerZ; }

  float getOuterZ() const { return theDoublets->z(theDoubletId, HitDoublets::outer); }

  float getInnerR() const { return theInnerR; }

  float getOuterR() const { return theDoublets->rv(theDoubletId, HitDoublets::outer); }

  float getInnerPhi() const { return theDoublets->phi(theDoubletId, HitDoublets::inner); }

  float getOuterPhi() const { return theDoublets->phi(theDoubletId, HitDoublets::outer); }

  void evolve(unsigned int me, CAStatusColl& allStatus) {
    allStatus[me].hasSameStateNeighbors = 0;
    auto mystate = allStatus[me].theCAState;

    for (auto oc : theOuterNeighbors) {
      if (allStatus[oc].getCAState() == mystate) {
        allStatus[me].hasSameStateNeighbors = 1;

        break;
      }
    }
  }

  void checkAlignmentAndAct(CAColl& allCells,
                            CAntuple& innerCells,
                            const float ptmin,
                            const float region_origin_x,
                            const float region_origin_y,
                            const float region_origin_radius,
                            const float thetaCut,
                            const float phiCut,
                            const float hardPtCut,
                            std::vector<CACell::CAntuplet>* foundTriplets) {
    int ncells = innerCells.size();
    int constexpr VSIZE = 16;
    int ok[VSIZE];
    float r1[VSIZE];
    float z1[VSIZE];
    auto ro = getOuterR();
    auto zo = getOuterZ();
    unsigned int cellId = this - &allCells.front();
    auto loop = [&](int i, int vs) {
      for (int j = 0; j < vs; ++j) {
        auto koc = innerCells[i + j];
        auto& oc = allCells[koc];
        r1[j] = oc.getInnerR();
        z1[j] = oc.getInnerZ();
      }
      // this vectorize!
      for (int j = 0; j < vs; ++j)
        ok[j] = areAlignedRZ(r1[j], z1[j], ro, zo, ptmin, thetaCut);
      for (int j = 0; j < vs; ++j) {
        auto koc = innerCells[i + j];
        auto& oc = allCells[koc];
        if (ok[j] && haveSimilarCurvature(
                         oc, ptmin, region_origin_x, region_origin_y, region_origin_radius, phiCut, hardPtCut)) {
          if (foundTriplets)
            foundTriplets->emplace_back(CACell::CAntuplet{koc, cellId});
          else {
            oc.tagAsOuterNeighbor(cellId);
          }
        }
      }
    };
    auto lim = VSIZE * (ncells / VSIZE);
    for (int i = 0; i < lim; i += VSIZE)
      loop(i, VSIZE);
    loop(lim, ncells - lim);
  }

  void checkAlignmentAndTag(CAColl& allCells,
                            CAntuple& innerCells,
                            const float ptmin,
                            const float region_origin_x,
                            const float region_origin_y,
                            const float region_origin_radius,
                            const float thetaCut,
                            const float phiCut,
                            const float hardPtCut) {
    checkAlignmentAndAct(allCells,
                         innerCells,
                         ptmin,
                         region_origin_x,
                         region_origin_y,
                         region_origin_radius,
                         thetaCut,
                         phiCut,
                         hardPtCut,
                         nullptr);
  }
  void checkAlignmentAndPushTriplet(CAColl& allCells,
                                    CAntuple& innerCells,
                                    std::vector<CACell::CAntuplet>& foundTriplets,
                                    const float ptmin,
                                    const float region_origin_x,
                                    const float region_origin_y,
                                    const float region_origin_radius,
                                    const float thetaCut,
                                    const float phiCut,
                                    const float hardPtCut) {
    checkAlignmentAndAct(allCells,
                         innerCells,
                         ptmin,
                         region_origin_x,
                         region_origin_y,
                         region_origin_radius,
                         thetaCut,
                         phiCut,
                         hardPtCut,
                         &foundTriplets);
  }

  int areAlignedRZ(float r1, float z1, float ro, float zo, const float ptmin, const float thetaCut) const {
    float radius_diff = std::abs(r1 - ro);
    float distance_13_squared = radius_diff * radius_diff + (z1 - zo) * (z1 - zo);

    float pMin = ptmin * std::sqrt(distance_13_squared);  //this needs to be divided by radius_diff later

    float tan_12_13_half_mul_distance_13_squared =
        fabs(z1 * (getInnerR() - ro) + getInnerZ() * (ro - r1) + zo * (r1 - getInnerR()));
    return tan_12_13_half_mul_distance_13_squared * pMin <= thetaCut * distance_13_squared * radius_diff;
  }

  void tagAsOuterNeighbor(unsigned int otherCell) { theOuterNeighbors.push_back(otherCell); }

  bool haveSimilarCurvature(const CACell& otherCell,
                            const float ptmin,
                            const float region_origin_x,
                            const float region_origin_y,
                            const float region_origin_radius,
                            const float phiCut,
                            const float hardPtCut) const {
    auto x1 = otherCell.getInnerX();
    auto y1 = otherCell.getInnerY();

    auto x2 = getInnerX();
    auto y2 = getInnerY();

    auto x3 = getOuterX();
    auto y3 = getOuterY();

    float distance_13_squared = (x1 - x3) * (x1 - x3) + (y1 - y3) * (y1 - y3);
    float tan_12_13_half_mul_distance_13_squared = std::abs(y1 * (x2 - x3) + y2 * (x3 - x1) + y3 * (x1 - x2));
    // high pt : just straight
    if (tan_12_13_half_mul_distance_13_squared * ptmin <= 1.0e-4f * distance_13_squared) {
      float distance_3_beamspot_squared =
          (x3 - region_origin_x) * (x3 - region_origin_x) + (y3 - region_origin_y) * (y3 - region_origin_y);

      float dot_bs3_13 = ((x1 - x3) * (region_origin_x - x3) + (y1 - y3) * (region_origin_y - y3));
      float proj_bs3_on_13_squared = dot_bs3_13 * dot_bs3_13 / distance_13_squared;

      float distance_13_beamspot_squared = distance_3_beamspot_squared - proj_bs3_on_13_squared;

      return distance_13_beamspot_squared < (region_origin_radius + phiCut) * (region_origin_radius + phiCut);
    }

    //87 cm/GeV = 1/(3.8T * 0.3)

    //take less than radius given by the hardPtCut and reject everything below
    float minRadius = hardPtCut * 87.f;  // FIXME move out and use real MagField

    auto det = (x1 - x2) * (y2 - y3) - (x2 - x3) * (y1 - y2);

    auto offset = x2 * x2 + y2 * y2;

    auto bc = (x1 * x1 + y1 * y1 - offset) * 0.5f;

    auto cd = (offset - x3 * x3 - y3 * y3) * 0.5f;

    auto idet = 1.f / det;

    auto x_center = (bc * (y2 - y3) - cd * (y1 - y2)) * idet;
    auto y_center = (cd * (x1 - x2) - bc * (x2 - x3)) * idet;

    auto radius = std::sqrt((x2 - x_center) * (x2 - x_center) + (y2 - y_center) * (y2 - y_center));

    if (radius < minRadius)
      return false;  // hard cut on pt

    auto centers_distance_squared = (x_center - region_origin_x) * (x_center - region_origin_x) +
                                    (y_center - region_origin_y) * (y_center - region_origin_y);
    auto region_origin_radius_plus_tolerance = region_origin_radius + phiCut;
    auto minimumOfIntersectionRange =
        (radius - region_origin_radius_plus_tolerance) * (radius - region_origin_radius_plus_tolerance);

    if (centers_distance_squared >= minimumOfIntersectionRange) {
      auto maximumOfIntersectionRange =
          (radius + region_origin_radius_plus_tolerance) * (radius + region_origin_radius_plus_tolerance);
      return centers_distance_squared <= maximumOfIntersectionRange;
    }

    return false;
  }

  // trying to free the track building process from hardcoded layers, leaving the visit of the graph
  // based on the neighborhood connections between cells.

  void findNtuplets(CAColl& allCells,
                    std::vector<CAntuplet>& foundNtuplets,
                    CAntuplet& tmpNtuplet,
                    const unsigned int minHitsPerNtuplet) const {
    // the building process for a track ends if:
    // it has no outer neighbor
    // it has no compatible neighbor
    // the ntuplets is then saved if the number of hits it contains is greater than a threshold

    if (tmpNtuplet.size() == minHitsPerNtuplet - 1) {
      foundNtuplets.push_back(tmpNtuplet);
    } else {
      unsigned int numberOfOuterNeighbors = theOuterNeighbors.size();
      for (unsigned int i = 0; i < numberOfOuterNeighbors; ++i) {
        tmpNtuplet.push_back((theOuterNeighbors[i]));
        allCells[theOuterNeighbors[i]].findNtuplets(allCells, foundNtuplets, tmpNtuplet, minHitsPerNtuplet);
        tmpNtuplet.pop_back();
      }
    }
  }

private:
  CAntuple theOuterNeighbors;

  const HitDoublets* theDoublets;
  const int theDoubletId;

  const float theInnerR;
  const float theInnerZ;
};

#endif  // RecoPixelVertexing_PixelTriplets_src_CACell_h