code: def _ic_matrix(ics, ic_i):
      
      cols, _ = ics.shape
      rows = len(ics[ic_i].iloc[0])
      ic_i_val = np.zeros((rows, cols))
  
      for idx, val in enumerate(ics.index):
          ic = ics.loc[val][ic_i]
  
          if len(ic) != rows:
              raise ValueError("The number of observations should be the same across all models")
  
          ic_i_val[:, idx] = ic
  
      return rows, cols, ic_i_val
docs: Store the previously computed pointwise predictive accuracy values (ics) in a 2D matrix.