Error using odearguments (line 95) returns a vector of length 2, but the length of initial conditions vector is 3. The vector returned by function and the initial conditions vector must have the same number of elements.

I am trying to make a couple of graphs with ODE functions, but it happens that I want to add 0.1 intervals to the graph from 0.001 to 1 but it shows the following error:

Error using odearguments (line 95)

CLASE2 returns a vector of length 2, but the length of initial conditions vector is 3. The vector returned by CLASE2 and

the initial conditions vector must have the same number of elements.

This is my function:

function dydt = clase2 (t,y)
Kso=0.153;
Kso1=0.135;
umax=0.253;
Kss=0.01;
Di=0.001;
Sen=2;
X=y(1); S=y(2);
u = (umax*X)/(Kss+S);
dXdt = (u*X)-(Di*X);
dSdt = ((-Kso*S*X)/(Kso1+S))-(Di*S)+(Di*Sen);
dydt = [dXdt dSdt]';

This is my script:

[t,x] = ode23('clase2',[0, 80],[0.001 0.01 1]);
plot(t,x(:,1));
xlabel('Tiempo (h)')
ylabel('Biomasa')
title('Biomasa')
figure
Di = 0.001;
plot(t,x(:,2));
xlabel('Tiempo (h)')
ylabel('Sustrato')
title('Sustrato')

[Walter Roberson]

The message is correct. Your dydt is a vector of length 2, but your initial conditions [0.001 0.01 1] is a vector of length 3.

You need to return a derivative for each boundary condition.

When I look at your initial condition [0.001 0.01 1] I have to wonder whether perhaps those values are intended to be three different values of a parameter that you are supposed to use in the equations, creating one plot for each of them?

[Dionisio Mendoza]

Thanks!

What I want to do is that in the two graphs I have already made there are 0.01 jumps that start at 0.001 and end at 1

[Walter Roberson]

[t,x] = ode23('clase2',[0, 80],[0.001 0.01 1]);

Should be something like

y0 = vector of two values 
tspan = [0, 0.001;0.01;1, 1:80];
[t, x] = ode23(@clase2, tspan, y0);

Answer 1

[Steven Lord]

Are you trying to control the times at which ode23 returns the solutions of your ODEs to make them more finely spaced? If so, don't change the initial condition vector. Change the tspan input instead, specifying a vector with more than two elements. If you had called ode23 with one output instead of two, you could have used the deval function to evaluate that existing solution at a different set of times.

If you want to solve the system of ODEs at different values of Di, parameterize your ODE function. The examples on that page use fzero but the ode23 documentation page includes an example showing how to use one of those techniques with ode23.

[Dionisio Mendoza]

I can not understand, i need to put another ecuation?