def computeEnvelope(self, placeCode):
    """
    Compute an envelope for use in suppressing border cells.
    :param placeCode: The place code representing the population the envelope
            will be used for.
    :return: A numpy array that can be elementwise-multiplied with activations
             for the given cell population to apply the envelope.
    """
    places = np.abs(placeCode - 0.5)
    envelope = [1 if p < 1 - self.envelopeWidth else
                      np.exp(-1.*self.envelopeFactor *
                      ((p - 1 + self.envelopeWidth)/self.envelopeWidth)**2)
                      for p in places]

    return np.asarray(envelope)