def _preSynapticTRNCells(self, i, j):
    """
    Given a relay cell at the given coordinate, return a list of the (x,y)
    coordinates of all TRN cells that project to it. This assumes a 3X3 fan-in.

    :param i, j: relay cell Coordinates

    :return:
    """
    xmin = max(i - 1, 0)
    xmax = min(i + 2, self.trnWidth)
    ymin = max(j - 1, 0)
    ymax = min(j + 2, self.trnHeight)
    trnCells = [
      (x, y) for x in range(xmin, xmax) for y in range(ymin, ymax)
    ]

    return trnCells
Given a relay cell at the given coordinate, return a list of the (x,y)
    coordinates of all TRN cells that project to it. This assumes a 3X3 fan-in.

    :param i, j: relay cell Coordinates

    :return: