code: def comb(A, B, C, sizeB, sizeC):
      # generate_knntriplets helper function
      # generate an array with all combinations of choosing
      # an element from A, B and C
      return np.vstack(
          (
              np.tile(A, (sizeB * sizeC, 1)).ravel(order="F"),
              np.tile(np.hstack(B), (sizeC, 1)).ravel(order="F"),
              np.tile(C, (1, sizeB)).ravel(),
          )
      ).T
  
file_path: metric-learn/metric_learn/constraints.py
imports: import numpy
  import warnings
  from sklearn.utils import check_random_state
  from sklearn.neighbors import NearestNeighbors
label_desc: Use image node_id 1 for calling a global function with example usage: comb(A, B, C, sizeB, sizeC) and returns: np