def GenerateAnnulusRZPhiToNode(nRCoords, nZCoords, phiPoints): 
  """
  Generate the map from r, z phi IDs to node IDs for a structured 3D linear
  tet annulus mesh
  """
 
  rzphiToNode = []
  index = 0
  for i in range(nRCoords): 
    rzphiToNode.append([])
    for j in range(nZCoords):
      rzphiToNode[i].append([])
      for k in range(phiPoints):
        rzphiToNode[i][j].append(index)
        index += 1
  
  return rzphiToNode