Matlab doesn run the program , says at the editor 'input argument might be unused ' for t

function dxdt = odefun(t, x)

dxdt = zeros(3,1);

dxdt(1) = - (8/3)*x(1) + x(2)*x(3);

dxdt(2) = - 10*x(2) + 10*x(3);

dxdt(3) = - x(3) - x(2)*x(1) + 28*x(2);

end

>> tspan = [0 20];

>> x0 = [20 -5 5];

>> [t,x]=ode45(@(t,x)odefun(t,x),tspan,x0);

Unrecognized function or variable 'odefun'.

Error in @(t,x)odefun(t,x)

Error in odearguments (line 92)

f0 = ode(t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 107)

odearguments(odeIsFuncHandle,odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);

Answer 1

[Bora Eryilmaz]

You have to save your odefun function into a MATLAB file with the name odefun.m.

The message "input argument might be unused ' for t" is just a warning that you can ignore. It is not your main error.

Alternatively, you can create a MATLAB script and use the following code in there. Note that the "local" function odefun is now in the same MATLAB script:

tspan = [0 20];
x0 = [20 -5 5];
[t,x]=ode45(@(t,x)odefun(t,x),tspan,x0);
ode45(@(t,x)odefun(t,x),tspan,x0); % For visualization

function dxdt = odefun(t, x)
dxdt = zeros(3,1);
dxdt(1) = - (8/3)*x(1) + x(2)*x(3);
dxdt(2) = - 10*x(2) + 10*x(3);
dxdt(3) = - x(3) - x(2)*x(1) + 28*x(2);
end

[Eleftherios]

I saved with this name odefun.m but when i write the code at the command window the program doesn't run . Again the same messages.

Unrecognized function or variable 'odefun'.

Error in @(t,x)odefun(t,x)

Error in odearguments (line 92)

f0 = ode(t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 107)

odearguments(odeIsFuncHandle,odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);

[Bora Eryilmaz]

You need to save only this part of the code in the file named odefun.m:

function dxdt = odefun(t, x)
dxdt = zeros(3,1);
dxdt(1) = - (8/3)*x(1) + x(2)*x(3);
dxdt(2) = - 10*x(2) + 10*x(3);
dxdt(3) = - x(3) - x(2)*x(1) + 28*x(2);
end

Then as long as the file's directory is on your MATLAB path or you are currently in that directory, you should be able to call it from another MATLAB file/script that contains:

tspan = [0 20];
x0 = [20 -5 5];
[t,x]=ode45(@(t,x)odefun(t,x),tspan,x0);
ode45(@(t,x)odefun(t,x),tspan,x0); % For visualization

Answer 2

[Jon]

If you have your odefun stored in it's own .m file then the syntax for calling ode45 is just

[t,x]=ode45(@odefun,tspan,x0);

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