code: def close(self, child):
          
          c = self.children[child]
          # flatten if children not None
          if c.children is not None and len(c.children) != 0:
              c.flatten()
  
          if c.value != 0. and not np.isnan(c.value):
              c.allocate(-c.value)
docs: Close a child position - alias for rebalance(0, child). This will also
          flatten (close out all) the child's children.
  
          Args:
              * child (str): Child, specified by name.