MATLAB: Plotting differential equations

differential equationsplotting

I would like to plot three differential equations in a graph and I don't know how to do it.

The equations are:

dCxdt=0.4*Cx*Cy/(2.5+Cx)

dCydt=-2.22*0.4*Cy*Cx/(2.5+Cy)-0.03*Cx

dCzdt=0.85*0.4*Cx*Cy/(2.5+Cy)

with initial values of: Cx=0.2, Cs=60, Cp=0

if any more information is needed please ask for it.

Thank you for your help

Best Answer

Please clarify your boundary conditions.

If they are Cx(0)=0.2, Cy(0)=0, Cz(0)=60, and if the equations are

diff(Cx(t), t) = .4*Cx(t)*Cy(t)/(2.5+Cx(t))
diff(Cy(t), t) = -.888*Cy(t)*Cx(t)/(2.5+Cy(t))-.3*Cy(t)
diff(Cz(t), t) = .340*Cy(t)*Cx(t)/(2.5+Cy(t))

then the overall solution is Cx(t)=0.2, Cy(t)=0, Cz(t)=60

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See ode45()

tspan = [0, 40];
ic = [80; 100];
[t, Z] = ode45(@odeFun, tspan, ic);
x = Z(:,1); % x solution
y = Z(:,2); % y solution
hold on
plot(t, x, 'ro-');
plot(t, y, 'bv-');
legend({'x', 'y'})
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    y = Z(2);
    
    dxdt = 0.5*x - 0.01*x*y;
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    dZdt = [dxdt; dydt];
end

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