Trying to graph two differential equations on same plot

T1=50+273.15;              %%k
T2=127+273.15;             %%k
Fao=2.5;            %%mol/min
P=10;               %%atm
k1=10^-4;           %%min^-1
R=8.314;       %j/k*mol
R1=8.206*10^-5*1000;         %%atm*dm^3/K*mol
E=85*1000;               %%j/mol
k2=k1*exp(E/R*(1/T1-1/T2)); %%min^-1
cao=P/(T2*R1);          %%mol/dm^3
ep=2+1-1;
xf=.90;
alpha=.001;       %%dm^3
volcstr=(Fao*xf)*(1+ep*xf)/(k2*cao*(1-xf)); %%dm^3
fun=@(x) Fao/(cao*k2)*(1+ep*x)./(1-x);
volpfr=integral(fun,0,xf);                  %%dm^3 

[x,y]=ode45(@(x,y) jallohwfun7(alpha,ep,xf,y,cao,k2,Fao),[0 500],[0 1]);
plot(x,y(:,1),'r','LineWidth',1);
      hold on;
      plot(x,y(:,2),'k','LineWidth',1);
      legend('Pressure', 'Conversion');
      xlabel('Volume [dm^3]');
      ylabel('Pressure [atm] & Conversion');
      title('Pressure and Conversion vs Volume ');

function dydt=jallohwfun7(alpha,ep,xf,y,cao,k2,Fao)

dydt=zeros(2,1);
dydt(1)=-alpha*(1+ep*xf)/2*y(1);
dydt(2)=k2*cao/Fao*(1-y(2))/(1+ep*y(2));

end

I want to graph two differential equations on same graph however i keep getting a straight line for both equations, which is incorrect.

Answer 1

[David Goodmanson]

Hi Rodrigo,

you have the following:

function dydt=jallohwfun7(alpha,ep,xf,y,cao,k2,Fao)
dydt=zeros(2,1);
dydt(1)=-alpha*(1+ep*xf)/2*y(1);
dydt(2)=k2*cao/Fao*(1-y(2))/(1+ep*y(2));
end

with initial conditions y(1) = 0, y(2) = 1. Plugging those in gives dy/dt(1) = 0, dy/dt(2) = 0 so the system never gets off the schneid. It just stays in the initial state.

[Rodrigo Blas]

Thank you for your help!