function v = tumor1(t, Y, Z, a,m,n,Kh,P,al,b,c,de,f,g,Kt)
v = zeros(3,1);

x = Y(1);
y = Y(2);
z = Y(3);
ylag = Z(:,1);

dxdt = a*min(1,(P-1000*n*x-10*m*y-10*n*z)/(1000*f*n*Kh))*x-a*x*((x+0.01*y)/Kh);
dydt = b*y*(min(1,(P-1000*n*x-10*m*y-10*n*z)/(1000*f*m*Kh))*min(1,g*max(0,z-al*y))-y/Kt);
dzdt = c*ylag(2)-de*z*z/y;
v = [dxdt; dydt; dzdt];

%# John Nagy model
%p a=1,m=.02,n=.01,kh=10,Kt=100,f=0.6667,P=110,al=.05,b=3,tau=3,c=.05,de=1,g=200
%x'  = a*min(1,(P-1000*n*x-10*m*y-10*n*z)/(1000*f*kh*n))*x-a*x*((x+0.01*y)/kh)
%y'  = b*y*(min(1,(P-1000*n*x-10*m*y-10*n*z)/(1000*f*kh*m))*min(1,g*max(0,z-al*y))-y/Kt)
%z'  = c*delay(y,tau)-de*z*z/y
%I x=9,y=.01,z=.001% 
%x - Mass of healthy cells in a single organ (in kg units)
% y - Mass of parenchyma (tumor) cells (10 gm units)
% z - Mass of microvessels within tumor (z/x = dimensionless microvascular density) (10 gm)
% Assume that maximum tumor mass is 1000 gm
% Assume that 50% of organ volume is extracellular fluid
% Multiply max term in y' equation by g because z is typically no more than 1/10th of 
% y which is typically no more than 1/10th of x, and g is typically > 100
% P-100*n*x-m*y-n*z (in the unit of 10 gm) is the total phosphorous in the 
% interstitial/blood fluid of organ. The organ fluid has a mass of 50% of 
% the organ, which is equal to 5000 gm, or 500 units (in 10 gm unit). Therefore
% (P-100*n*x-m*y-n*z)/500 describes the free phosphorous percentage content in 
% interstitial/blood fluid of organ.
% K=maximum tumor mass units (in 10 gm).
% a maximum growth rate of organ cells under optimal conditions
% n percentage of phosphorous content in healthy cells within the organ
% m same for tumor cells
% b max growth rate of parenchyma (tumor) cells in optimal conditions
% Ph is total phosphorous within system
% al mass of tumor cells that a unit of blood vessels can just barely maintain
% c rate at which new microvessels arise within tumor
% de crowding parameter for microvessels