docs: def get_all_synIdx(self):
          """
          Auxilliary function to set up class attributes containing
          synapse locations given as LFPy.Cell compartment indices
  
          This function takes no inputs.
  
  
          Parameters
          ----------
          None
  
  
          Returns
          -------
          synIdx : dict
              `output[cellindex][populationindex][layerindex]` numpy.ndarray of
              compartment indices.
  
  
          See also
          --------
          Population.get_synidx, Population.fetchSynIdxCell
          """
          tic = time()
  
          #containers for synapse idxs existing on this rank
          synIdx = {}
  
  
          #ok then, we will draw random numbers across ranks, which have to
          #be unique per cell. Now, we simply record the random state,
          #change the seed per cell, and put the original state back below.
          randomstate = np.random.get_state()
  
          for cellindex in self.RANK_CELLINDICES:
              #set the random seed on for each cellindex
              np.random.seed(self.POPULATIONSEED + cellindex)
  
              #find synapse locations for cell in parallel
              synIdx[cellindex] = self.get_synidx(cellindex)
  
          #reset the random number generator
          np.random.set_state(randomstate)
  
          if RANK == 0:
              print('found synapse locations in %.2f seconds' % (time()-tic))
  
          #print the number of synapses per layer from which presynapse population
          if self.verbose:
              for cellindex in self.RANK_CELLINDICES:
                  for i, synidx in enumerate(synIdx[cellindex]):
                      print('to:\t%s\tcell:\t%i\tfrom:\t%s:' % (self.y,
                                                  cellindex, self.X[i]),)
                      idxcount = 0
                      for idx in synidx:
                          idxcount += idx.size
                          print('\t%i' % idx.size,)
                      print('\ttotal %i' % idxcount)
  
          return synIdx