function [TD,TO,CH,t,x,CS,ND]=demand(TD,TO,CH,CS,ND,t,x,h,p,l,L,s)
ND=ND+1;          %increment the number demanded by 1
CH=CH+x*h*(TD-t);  %increment holding cost since last event
t=TD;              %update clock time
if (x==0)          
   CS=CS+p;        %if no stock, add penalty p for unsatisfied demand
elseif (x==s)       %if stock=s, place order 
   TO=t+L;           % schedule time of arrival of order TO
else
end
TD=TD+exprnd(1/l,1,1);    %schedule next demand
x=max(0,x-1);             %reduce stock by 1 if positive