code: def _normalize_functions(y_values_list, t_values):
      """Normalize list of functions by their integral value
  
      Parameters
      ----------
      y_values_list : `list` of np.ndarray
          y values of the list of function we want to normalize
  
      t_values : `np.ndarray`
          t values shared by all functions given with y_values_list
  
      Returns
      -------
      normalized_y_values_list : `list` of np.ndarray
          Normalized y values of the given list of function
  
      normalizations : `np.ndarray`
          Normalization factors that have been used
      """
      y_values_list = np.array(y_values_list)
      normalizations = [
          1.0 / np.trapz(y_values, t_values)
          for y_values in y_values_list
      ]
      normalized_y_values_list = (y_values_list.T * normalizations).T
      return normalized_y_values_list, normalizations
  
file_path: tick/tick/plot/plot_hawkes.py
imports: import matplotlib.pyplot
  import numpy
  from mpl_toolkits.axes_grid1 import make_axes_locatable
  from tick.plot.plot_utilities import share_x, share_y
label_desc: Use image node_id 4 for calling a global function with example usage: _normalize_functions(y_values_list, t_values) and returns: normalized_y_values_list,  normalizations