code: def _initialize(self, funs_to_tally, length):
          
  
          chain = self.nchains
          self._chains[chain] = self._h5file.create_group(
              '/', 'chain%d' % chain, 'chain #%d' % chain)
  
          for name, fun in six.iteritems(funs_to_tally):
  
              arr = np.asarray(fun())
  
              assert arr.dtype != np.dtype('object')
  
              array = self._h5file.createEArray(
                  self._chains[chain], name,
                  tables.Atom.from_dtype(arr.dtype), (0,) + arr.shape,
                  filters=self.filter)
  
              self._arrays[chain, name] = array
              self._traces[name] = Trace(name, getfunc=fun, db=self)
              self._traces[name]._initialize(self.chains, length)
  
          self.trace_names.append(list(funs_to_tally.keys()))
docs: Create a group named ``chain#`` to store all data for this chain.