def indexCube(nodes, gridSize, n=None):
    """
    Returns the index of nodes on the mesh.


    Input:
       nodes     - string of which nodes to return. e.g. 'ABCD'
       gridSize  - size of the nodal grid
       n         - number of nodes each i,j,k direction: [ni,nj,nk]


    Output:
       index  - index in the order asked e.g. 'ABCD' --> (A,B,C,D)

    TWO DIMENSIONS::

      node(i,j)          node(i,j+1)
           A -------------- B
           |                |
           |    cell(i,j)   |
           |        I       |
           |                |
          D -------------- C
      node(i+1,j)        node(i+1,j+1)


    THREE DIMENSIONS::

            node(i,j,k+1)       node(i,j+1,k+1)
                E --------------- F
               /|               / |
              / |              /  |
             /  |             /   |
      node(i,j,k)         node(i,j+1,k)
           A -------------- B     |
           |    H ----------|---- G
           |   /cell(i,j)   |   /
           |  /     I       |  /
           | /              | /
           D -------------- C
      node(i+1,j,k)      node(i+1,j+1,k)

    """

    assert type(nodes) == str, "Nodes must be a str variable: e.g. 'ABCD'"
    assert isinstance(gridSize, np.ndarray), "Number of nodes must be an ndarray"
    nodes = nodes.upper()
    # Make sure that we choose from the possible nodes.
    possibleNodes = 'ABCD' if gridSize.size == 2 else 'ABCDEFGH'
    for node in nodes:
        assert node in possibleNodes, "Nodes must be chosen from: '%s'" % possibleNodes
    dim = gridSize.size
    if n is None:
        n = gridSize - 1

    if dim == 2:
        ij = ndgrid(np.arange(n[0]), np.arange(n[1]))
        i, j = ij[:, 0], ij[:, 1]
    elif dim == 3:
        ijk = ndgrid(np.arange(n[0]), np.arange(n[1]), np.arange(n[2]))
        i, j, k = ijk[:, 0], ijk[:, 1], ijk[:, 2]
    else:
        raise Exception('Only 2 and 3 dimensions supported.')

    nodeMap = {'A': [0, 0, 0], 'B': [0, 1, 0], 'C': [1, 1, 0], 'D': [1, 0, 0],
               'E': [0, 0, 1], 'F': [0, 1, 1], 'G': [1, 1, 1], 'H': [1, 0, 1]}
    out = ()
    for node in nodes:
        shift = nodeMap[node]
        if dim == 2:
            out += (sub2ind(gridSize, np.c_[i+shift[0], j+shift[1]]).flatten(), )
        elif dim == 3:
            out += (sub2ind(gridSize, np.c_[i+shift[0], j+shift[1], k+shift[2]]).flatten(), )

    return out
dataset/ETHPy150Open simpeg/simpeg/SimPEG/Utils/curvutils.py/indexCube/original