def set **nn
      key = identify **nn
      @key = if key.nil? then key
             elsif @hash.has_key? key then key
             else raise "No simulation identified by #{key}!" end
    end
def set **nn
      key = identify **nn
      @key = if key.nil? then key
             elsif @hash.has_key? key then key
             else raise "No simulation identified by #{key}!" end
    end
A simulation is identified either by its name (if named), or by its
 parameters and settings (:net, :cc, :imc, :ssc).