# How to Graph more than one ODE on a plot

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Will Jeter on 4 Nov 2020
Answered: Reshma Nerella on 10 Nov 2020
I can't get my two functions for my ODEs to graph on the same plot. I'm not sure how get these to work with each other.
Volume = [0,2500];
Conversion = ;
[V, X] = ode45(@odefun3,Volume,Conversion);
figure
plot(V,X)
xlabel('Volume')
ylabel('Conversion')
legend('No Inlet','Medium Inlet')
function dXdV = odefun3(V,X)
CA0 = 2/0.082/1100;
CI0 = CA0;
Theta = 0;
FA0 = 10;
CA01 = (CA0+CI0)/(Theta+1);
e = 1/(1+Theta);
T0 = 1100;
dHrx = 80000;
CpA = 170;
CpI = 200;
T = (X*(-dHrx)+(CpA+Theta*CpI)*T0)/(CpA+Theta*CpI);
k = exp(34.34-(34222/T));
ra = -k*CA01*(1-X)*T0/(1+e*X)/T;
dXdV = -ra/FA0;
end
[V, X] = ode45(@odefun4,Volume,Conversion);
function dXdV = odefun4(V,X)
CA0 = 2/0.082/1100;
CI0 = CA0;
Theta = 0.1;
FA0 = 10;
CA01 = (CA0+CI0)/(Theta+1);
e = 1/(1+Theta);
T0 = 1100;
dHrx = 80000;
CpA = 170;
CpI = 200;
T = (X*(-dHrx)+(CpA+Theta*CpI)*T0)/(CpA+Theta*CpI);
k = exp(34.34-(34222/T));
ra = -k*CA01*(1-X)*T0/(1+e*X)/T;
dXdV = -ra/FA0;
end

Reshma Nerella on 10 Nov 2020
Hi,
As per my understanding, you want to plot 2 ODEs on same graph. Use can use hold command to add many plots on existing axes.
You can do it this way:
[V, X] = ode45(@odefun3,Volume,Conversion);
plot(V,X);
xlabel('Volume');
ylabel('Conversion');
hold on % to add new plot to same axes
[V, X] = ode45(@odefun4,Volume,Conversion);
plot(V,X);
xlabel('Volume');
ylabel('Conversion');
hold off % to prevent other plots using the same axes
legend('No Inlet','Medium Inlet'); % You can add legends for the plots at a time.
Hope this helps!