Ode45 not working in matlab 2021b

I'm workin on a project for university, and I got a problem:

I'm getting an error with ode45, and I got no clue how to fix it.

Could you lend me a hand?

Here's the code:

function pendul(~)
figure
disp('')
disp('DAMPED PENDULUM MOTION DESCRIBED BY')
disp('theta"(t)+0.2*theta''(t)+sin(theta) = 0')
zdot=inline('[z(2);-0.2*z(2)-sin(z(1))]','t','z');
ops=odeset('reltol',1e-5,'abstol',1e-5);
if nargin==0
while 1, close, disp(' ')
disp('Select the angular velocity at the lowest')
disp('point. Values of 2.42 or greater push the')
disp( 'the pendulum over the top. Input zero to stop.')
 w0=input('w0 = ? > ');
 
if isempty(w0) || w0==0
disp(' '), disp('All Done'), disp(' '), return
end
disp(' ')
t=input(['Input a vector of time values ', '(Try 0:.1:30) > ? ']);
 
disp(' ')
titl=input('Input a title for the graphs : ','s');
disp(' '), disp('Input 1 to leave images of all positions shown')
trac=input( 'in the animation, otherwise input 0 > ? ');
theta0=0; z0=[theta0;w0];
[t,th]=ode45(zdot,t,z0,ops);
animpen(t,th(:,1),titl,.05,trac)
end
else
 
tmax=30; n=351; t=linspace(0,tmax,n);
 
disp(' ')
disp('Press return to see two examples'), pause
 
w0=2.42; W0=num2str(w0);
[t,th]=ode45(zdot,t,[0;w0],ops);
titl=['PUSHED OVER THE TOP FOR W0 = ',W0];
animpen(t,th(:,1), titl,.05), pause(2)
w0=2.41; W0=num2str(w0);
[t,th]=ode45(zdot,t,[0;w0],ops);
titl=['NEARLY PUSHED OVER THE TOP FOR W0 = ',W0];
animpen(t,th(:,1),titl,.05)
close, disp(' '), disp('All Done'), disp(' ')

end

And I'm getting this error:

Error using inline/horzcat
Too many output arguments.

Error in odefcncleanup (line 15)
    [~,oldFcnFun] = evalc(['@' oldFcn]);

Error in ode45 (line 265)
odeFcn_main = odefcncleanup(FcnUsed,odeFcn,odeArgs);

Error in pendul (line 50)
[t,th]=ode45(zdot,t,z0,ops);

Any help would be much apreciated :D

[Steven Lord]

Stop using the inline function. Its use has been discouraged for pretty close to two decades now. It remains for backwards compatibility. As its documentation page suggests, use function handles instead. [Anonymous functions are a type of function handle.]

Answer 1

[VBBV]

zdot=inline('[z(2);-0.2*z(2)-sin(z(1))]','t','z')

Check your zdot function. There is no variable with t defined in it.

[VBBV]

You also need to use this syntax for ode45

[t,th]=ode45(@(t,z) zdot,t,z0,ops)

[Marcus Rost]

I tried replacing it, but I'm still getting this error:

Error using odearguments (line 95)
@(T,Z)ZDOT returns a vector of length 1, but the length of initial conditions vector is 2. The vector
returned by @(T,Z)ZDOT and the initial conditions vector must have the same number of elements.

Error in ode45 (line 106)
  odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

Error in pendul (line 50)
[t,th]=ode45(@(t,z)zdot,t,z0,ops);

[VBBV]

It seems you are entering time input longer than z0. Enter initial and final values only. E.g [0 10] between 0 and 10 sec enter z0 as [theta0 w0]

[Torsten]

zdot = @(t,z)[z(2);-0.2*z(2)-sin(z(1))];

instead of

zdot = inline('[z(2);-0.2*z(2)-sin(z(1))]','t','z');

[Marcus Rost]

Tried. Same error

[Torsten]

Please show the modified code.

And in a first attempt don't read w0 and t from input, but prescribe them as

w0 = 3.0;

t = 0:0.1:10

e.g.