def to_a type=String
      if type == String
        return self.to_s
      elsif type == Array
        return self.to_ary
      elsif type == Matrix
        return self.to_matrix
      else
        return nil
      end
    end
def to_a type=String
      if type == String
        return self.to_s
      elsif type == Array
        return self.to_ary
      elsif type == Matrix
        return self.to_matrix
      else
        return nil
      end
    end
== Parameters:
 type::
   It specify the return. It may be String or Array.

 == Returns:
 String, Array, nil (see type::)

 == Errors:
 nil return occures only if the parameter types:: is not supported.