docstr: Returns coefficients corresponding to a bell shaped relative
  incidence of max value equal to `amplitude`. If `cut` is greater than 0,
  the relative incidence will be null on [`cut`, `n_intervals`]. The
  effect starts at `lag` interval, and lasts `width` intervals.
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code: def bell_shaped_effect(self, amplitude, width, lag=0, cut=0):
      """Returns coefficients corresponding to a bell shaped relative
      incidence of max value equal to `amplitude`. If `cut` is greater than 0,
      the relative incidence will be null on [`cut`, `n_intervals`]. The
      effect starts at `lag` interval, and lasts `width` intervals.
      """
      self._check_params(lag, width, amplitude, cut)
      if width % 2 == 0:
          width += 1
      effect = norm(0, width / 5).pdf(np.arange(width) - int(width / 2))
      return self._create_risk_curve(effect, amplitude, cut, width, lag)
  
imports: from operator import itemgetter
  import numpy
  import scipy.sparse
  from scipy.sparse import csr_matrix
  from tick.base.simulation import Simu
  from tick.hawkes import SimuHawkesExpKernels, SimuHawkesMulti
  from tick.preprocessing import LongitudinalFeaturesLagger
  from itertools import permutations
  from copy import deepcopy
  from scipy.stats import beta, norm
label_desc: Use image node_id 3 for calling the CustomEffects obj's underlying member method code with example usage: obj.bell_shaped_effect(amplitude, width, lag, cut) and returns: self