'Accumulate some connections.'

def accumulate(self, con_idx, csd_xy):

    denom = np.abs(csd_xy)
    z_denom = np.where((denom == 0.0))
    denom[z_denom] = 1.0
    this_acc = (csd_xy / denom)
    this_acc[z_denom] = 0.0
    self._acc[con_idx] += this_acc
