docs: def calc_lfp(self):
          """ Sum all the LFP contributions from every cell type.
          """
  
          LFParray = np.array([])
          LFPdict = {}
  
          i = 0
          for y in self.y:
              fil = os.path.join(self.populations_path,
                                 self.output_file.format(y, 'LFP.h5'))
  
              f = h5py.File(fil)
  
              if i == 0:
                  LFParray = np.zeros((len(self.y),
                                      f['data'].shape[0], f['data'].shape[1]))
  
              #fill in
              LFParray[i, ] = f['data'].value
  
              LFPdict.update({y : f['data'].value})
  
              f.close()
  
              i += 1
  
          return LFPdict,  LFParray.sum(axis=0)