How can I solve this vector lenght problem?

Hi everyone!

It's been a long time since I used MATLAB for the last time. Unfortunatelly, I got rusty and I'm trying to make some examples to brush up my skills. One of this example drove into a bug that I have no idea what can be and how to solve it. I'm trying to use the ODE45 function (Rugge Kutta Method) but I got this error alert.

@(T,Y)TANKMODEL(T,Y) returns a vector of length 1, but the length of initial conditions vector is 2. The vector returned by @(T,Y)TANKMODEL(T,Y) and the initial conditions vector must have the same number of elements.

Can someone give me a north to solve this?

My code is:

clc;
close all;
format long
%Rugge Kutta Method 
tspan = [0 5];
IC = [0 0];
[t,y] = ode45(@(t,y)tankmodel(t,y),tspan ,IC);
%Grafica
figure
plot(t,y)
title('Carbon Concentration');
xlabel('Time (s)');
ylabel('Concentration mg/m^3');

function dydt = tankmodel(t,y,z)

format long
%%%Dataset Parameters 
Wgrill = 500; Qink =  100; Cink = 2;QE =  25;CE = 2;Ve= 840;Vk= 280;Ee= 25;Ek= 25;
Qoutk = Qink;
Qoute = Qink + QE;
%  Equations
dydt = ((Wgrill + Qink*Cink - Qoutk*y + Ee*z - Ek*y)/Vk);
y(1)= 0;
dzdt = ((QE*CE + Qoutk*y - Qoute*z + Ek*y - Ee*z)/Ve);
z(1) = 0;
end

Answer 1

[Star Strider]

Change your ‘tankmodel’ function to this and it works:

function dydt = tankmodel(t,yv)
format long
%%%Dataset Parameters 
Wgrill = 500; Qink =  100; Cink = 2;QE =  25;CE = 2;Ve= 840;Vk= 280;Ee= 25;Ek= 25;
Qoutk = Qink;
Qoute = Qink + QE;
y = yv(1);
z = yv(2);
%  Equations
dydt(1,:) = ((Wgrill + Qink*Cink - Qoutk*y + Ee*z - Ek*y)/Vk);
dydt(2,:) = ((QE*CE + Qoutk*y - Qoute*z + Ek*y - Ee*z)/Ve);
end

[Thiago Brito]

Thank you a lot! Just save my day!

Just one last question. Does it mean that the lenght of the vector is controlled by this part "dydt(1,:)"?

[Star Strider]

As always, my pleasure!

I am not certain what you are asking.

The time vector length is controlled by the ‘tspan’ argument.

The ‘y’ vector and the derivative your function returns (here ‘dydt’) are dictated by the function you are integrating. Here, both are (2x1) vectors.

[madhan ravi]

+1 @ Star Strider I learn something in your answers each time :)