% 1.731 Irrigation efficiency example
		% This program evaluates and plots net revenue (objective) vs. irrigation efficiency
		%
		% Problem inputs
		p=0.2    % crop market price in $ kg^-1
		Y0=5000  % maximum yield in kg ha^-1 yr^-1
		Sa=300   % applied water salinity in mg L^-1
		c=10  % applied water cost coef. in $ (ham)^-1 yr^-1
		Smax=1000 % maximum crop salinity in mg L^-1
				%
		% Plot objective function
		e=0.01*(10:50);   % efficiency range
		Yfactor=zeros(1,length(e))
		S=Sa./(1-e);    % root zone salinity
		Qa=3./e;        % applied water
		Sok=S<Smax
		Yfactor(Sok)=(1-S(Sok)./Smax).^3  % yield response function
		revenue=p*Y0*Yfactor
		cost=c*Qa
		F=revenue - cost
		close all
		figure
		plot(e,F,'b',e,revenue,'r',e,cost,'g')
		%
		% Identify optimum
		optf=max(F)    
		opte=0.1+0.01*(find(F==optf)-1)
           
ax(F)    
		opte=0.1+0.01*(find(F==optf)-1)