MATLAB: How to plot component curves for system of differential equations? I keep getting errors for this compartment model

ode45

F=@(t,x) [-4*x(1)+4*x(2); x(1)-6*x(2)+3*x(3)+2; x(1)+2*x(2)-8*x(3)+5];

[t,x]=ode45(F,[0 3], [0 10]);

plot(t, x(:,1), t, x(:,2), t, x(:,3))

Best Answer

You have to supply the same number of initial conditions to the ODE solver as you have variables in your ODE equation. Assuming you only want ‘x(3)’ to have anything in it at the start, this works:

[t,x]=ode45(F,[0 3], [0 0 10]);

The rest of your code is unchanged, although you might want to add this after your plot call:

legend('C_1(t)', 'C_2(t)', 'C_3(t)', 'Location','NE')

Related Solutions

MATLAB: Is there an easy way to make numerical simulations of the ODE of the form dx1/dt=x1(2-x1-x2), dx2/dt=x2(3-x1-x2-x3) for any xn

 See code comments for answers.  
clear variables
close all;
% dx must have 5 terms for n = 5
% the number terms in system equations
% must be the same as the number of 
% elements in your dx vector.
% Remember your dot before *
dx = @(t,x) [x(1);x(1).*(2-x(1)-x(2)); 
             x(2).*(3-x(1)-x(2)-x(3)); 
             x(3).*(3-x(2)-x(3)-x(4)); 
             x(4).*(3-x(3)-x(4)-x(5))]; 
tspan=[0 15]; 
x0=[0 2 0 3 0]; % same for the initial vector.
[t,x] = ode45(dx, tspan, x0); 
figure(1)
plot(t, x);

MATLAB: Error using odarguments: Inputs must be floats, namely single or double: ode45

ode45 is a numerical solver. There is no need to define the symbolic variable inside the function. Also, the ODE state variable is 'y', not 'x'. Change the function definition to this

function dx = vpd1(t,y)
b = .66;
beta = .79;
C = 203;
K = 543;
d = 2.17;
delta = .36;
dx = [b*y(1)*((C-y(1)-d*y(2))/C) ; beta*y(2)*((K-y(2)-delta*y(1))/K)];
end

Best Answer

Related Solutions

MATLAB: Is there an easy way to make numerical simulations of the ODE of the form dx1/dt=x1(2-x1-x2), dx2/dt=x2(3-x1-x2-x3) for any xn

MATLAB: Error using odarguments: Inputs must be floats, namely single or double: ode45

Related Question