code: def _cutoff(self, coeffs, vscale):
          
          bnd = self._threshold(vscale)
          inds  = np.nonzero(abs(coeffs) >= bnd)
          if len(inds[0]):
              N = inds[0][-1]
          else:
              N = 0
          return N+1
docs: Compute cutoff index after which the coefficients are deemed negligible.