a = 1/3;   % probability of a customer each day
  days_for_delivery = 2;   % days from order to delivery of new tanks

  stock = 1;   % number of tanks in stock
  deliv = -1;  % number of days until delivery of tank on order
               % -1 means none on order

  total_cust = 0;
  total_sold = 0;
  total_lost = 0;

  disp(' ')
  disp('   week  day   stock  cust  sold  lost')
  disp(' ')

  for week = 1:3
    for day = 1:7
      sold = 0;
      lost = 0;
      if deliv == 0 
             stock = stock+1;   % a new tank is delivered
	     end
      if deliv >= 0
	     deliv = deliv-1;   % days till next delivery
	     end


      random_num = rand(1);     % generate random number 
      if random_num < a         % use this number to tell if a customer arrived
         customers = 1;
	else
	 customers = 0;
	end
      
      if customers==1
         if stock>0             % we have a tank to sell the customer
	    sold = sold+1;
	    stock = stock-1;
	    if deliv < 0
	       deliv = days_for_delivery;  % we sold a tank and now order 
	                                 % another one.
	       end
	  else
	    lost = lost+1;      % we didn't have a tank and lost a customer
	  end
	end
    
      % keep track of total statistics:
      total_cust = total_cust + customers;
      total_sold = total_sold + sold;
      total_lost = total_lost + lost;

      disp([week day stock customers sold lost]);   % display results for 
                                                    % this day
      end
    end

  end
  disp(' ')
  disp('total over entire simultation:')
  disp(' ')
  disp('   customers   sold        lost')
  disp(sprintf('%8.0f  %8.0f  %8.0f ', ...
      total_cust, total_sold, total_lost))
  disp(' ')
  fraction_served = total_sold / total_cust;