code: import numpy as np
  import scipy
  from scipy.spatial.distance import cdist
  import lap  # 0.4.0
  
  from cython_bbox import bbox_overlaps as bbox_ious
  from . import kalman_filter
  
  def merge_matches(m1, m2, shape):
      O,P,Q = shape
      m1 = np.asarray(m1)
      m2 = np.asarray(m2)
  
      M1 = scipy.sparse.coo_matrix((np.ones(len(m1)), (m1[:, 0], m1[:, 1])), shape=(O, P))
      M2 = scipy.sparse.coo_matrix((np.ones(len(m2)), (m2[:, 0], m2[:, 1])), shape=(P, Q))
  
      mask = M1*M2
      match = mask.nonzero()
      match = list(zip(match[0], match[1]))
      unmatched_O = tuple(set(range(O)) - set([i for i, j in match]))
      unmatched_Q = tuple(set(range(Q)) - set([j for i, j in match]))
  
      return match, unmatched_O, unmatched_Q
  
  
  def linear_assignment(cost_matrix, thresh):
      if cost_matrix.size == 0:
          return np.empty((0, 2), dtype=int), tuple(range(cost_matrix.shape[0])), tuple(range(cost_matrix.shape[1]))
      matches, unmatched_a, unmatched_b = [], [], []
      cost, x, y = lap.lapjv(cost_matrix, extend_cost=True, cost_limit=thresh)
      for ix, mx in enumerate(x):
          if mx >= 0:
              matches.append([ix, mx])
      unmatched_a = np.where(x < 0)[0]
      unmatched_b = np.where(y < 0)[0]
      matches = np.asarray(matches)
      return matches, unmatched_a, unmatched_b
  
  
  def ious(atlbrs, btlbrs):
      """
      Compute cost based on IoU
      :type atlbrs: list[tlbr] | np.ndarray
      :type atlbrs: list[tlbr] | np.ndarray
  
      :rtype ious np.ndarray
      """
      ious = np.zeros((len(atlbrs), len(btlbrs)), dtype=np.float)
      if ious.size == 0:
          return ious
  
      ious = bbox_ious(
          np.ascontiguousarray(atlbrs, dtype=np.float),
          np.ascontiguousarray(btlbrs, dtype=np.float)
      )
  
      return ious
  
  
  def iou_distance(atracks, btracks):
      """
      Compute cost based on IoU
      :type atracks: list[STrack]
      :type btracks: list[STrack]
  
      :rtype cost_matrix np.ndarray
      """
  
      if (len(atracks)>0 and isinstance(atracks[0], np.ndarray)) or (len(btracks) > 0 and isinstance(btracks[0], np.ndarray)):
          atlbrs = atracks
          btlbrs = btracks
      else:
          atlbrs = [track.tlbr for track in atracks]
          btlbrs = [track.tlbr for track in btracks]
      _ious = ious(atlbrs, btlbrs)
      cost_matrix = 1 - _ious
  
      return cost_matrix
  
  def embedding_distance(tracks, detections, metric='cosine'):
      """
      :param tracks: list[STrack]
      :param detections: list[BaseTrack]
      :param metric:
      :return: cost_matrix np.ndarray
      """
  
      cost_matrix = np.zeros((len(tracks), len(detections)), dtype=np.float)
      if cost_matrix.size == 0:
          return cost_matrix
      det_features = np.asarray([track.curr_feat for track in detections], dtype=np.float)
      track_features = np.asarray([track.smooth_feat for track in tracks], dtype=np.float)
      cost_matrix = np.maximum(0.0, cdist(track_features, det_features)) # Nomalized features
  
      return cost_matrix
  
  
  def fuse_motion(kf, cost_matrix, tracks, detections, only_position=False, lambda_=0.98):
      if cost_matrix.size == 0:
          return cost_matrix
      gating_dim = 2 if only_position else 4
      gating_threshold = kalman_filter.chi2inv95[gating_dim]
      measurements = np.asarray([det.to_xyah() for det in detections])
      for row, track in enumerate(tracks):
          gating_distance = kf.gating_distance(
              track.mean, track.covariance, measurements, only_position, metric='maha')
          cost_matrix[row, gating_distance > gating_threshold] = np.inf
          cost_matrix[row] = lambda_ * cost_matrix[row] + (1-lambda_)* gating_distance
      return cost_matrix
  
apis: scipy.spatial.distance.cdist numpy.empty numpy.ascontiguousarray numpy.asarray numpy.where