def update
    respond_to do |format|
      emitter_params = params[@emitter_name.to_sym].inject({}) do |memo, tuple|
        param_key, param_value = tuple # param_key = :fuel_efficiency_in_miles_per_gallon ; param_value = "10,000"
        memo.merge({param_key => param_key.sanitize_if_numeric})
      end
      if @emitter.update_attributes(emitter_params)
        format.html do
          flash[:notice] = "#{@emitter.name} was successfully updated."
          redirect_to(@emitter)
        end
        format.xml  { head :ok }
        format.js   { render :template => 'emitters/update' }
      else
        format.html do
          if @characteristic
            render :template => "characteristics/edit"
          else
            render :text => "there was an error updating the #{@emitter_name.humanize.downcase} object as a whole, but there is no general edit page right now"
          end
        end
        format.xml  { render :xml => @emitter.errors, :status => :unprocessable_entity }
        format.js do # currently only used for renaming
          @emitter.name = @emitter.name_was if @emitter.name_changed? # this is kind of brittle
          render :template => 'emitters/update'
        end
      end
    end
  end