def disveclayers(self, x, y, layers, aq=None):
        '''Returns two arrays of size len(layers)
        only used in building equations'''
        if aq is None: aq = self.model.aq.find_aquifer_data(x, y)
        qxqy = self.disvec(x, y, aq)
        rv = np.sum(qxqy[:,np.newaxis,:] * aq.eigvec, 2)
        return rv[:,layers]
Returns two arrays of size len(layers)
        only used in building equations