code: def cull(data,index,min=None,max=None):    
      
  
      ret = data
  
      if min is not None:
          ret = ret[ret[:,index] > min,:]
  
      if max is not None:
          ret = ret[ret[:,index] < max,:]
      
      return ret
docs: Sieve an emcee clouds by excluding walkers with search variable 'index'
      smaller than 'min' or larger than 'max'.