Parse error at zeta.

I am trying to solve a differential equation using MATLAB however I am having trouble. there is a red error next to Zeta- the error is as follows:

This statement is not inside any function. Parse error at zeta. usage might be invalid MATLAB syntax

Thank you.

function dydt= odefcn(t,y,f,r,zeta)
dydt=zeros(2,1);
dydt(1)=y(2);
dydt(2)=fsin(r*t)-2.\z.y(2)-sin(y);

end

%parameters and initial conditions
zeta = 0.5; 
f = 0.40 + (0.1: 0.1: 0.4);
r = (0.3: 0.3: 1.5);
y(0)=0.5;
dy/dt(0)=0;
tspan = [0 1000]


options = odeset('RelTol',1e-6,'AbsTol' 1e-9 1e-9]);
[t,y] = ode45(@(t,y) odefcn(t,y,f,r,zeta), tspan, y0);

[the cyclist]

I edited your question, to make what you posted into a code block, and it ran without an error.

Do you get this problem with a fresh restart of MATLAB?

Can you post the full code that gives the error, and the complete error message (including line number, etc.)?

[Abdul Mirza]

Okay I've posted the full code in now.

I haven't tried running the code with a a MATLAB restart.

[Abdul Mirza]

Can you please help me with this?

Answer 1

[Star Strider]

There appear to be errors in ‘odefcn’ that need to be addressed.

I have no idea if ‘f’ and ‘r’ are to be evaluated together (as I did here), or if they need to be created using ndgrid as:

[fm,rm] = ndgrid(f,r);

and then evaluated as:

fv = fm(:);

rv = rm(:);

with:

N = numel(fv);

for k = 1:N

[t,y{k}] = ode45(@(t,y) odefcn(t,y,fv(k),rv(k),zeta), tspan, y0);

end

so every value of each is evalueated with evary value of the other, so I defer that to you.

%parameters and initial conditions
zeta = 0.5; 
% f = 0.40 + (0.1: 0.1: 0.4)
N = 5;
f = linspace(0.4, 0.8, N);
% r = (0.3: 0.3: 1.5)
r = linspace(1.3, 1.5, N);
% y(0)=0.5;
% dydt(0)=0;
y0 = [0.5, 0];
% tspan = [0 1000];
tspan = linspace(0, 1000, 250);

options = odeset('RelTol',1e-6,'AbsTol', 1e-9);
for k = 1:N
    [t,y{k}] = ode45(@(t,y) odefcn(t,y,f(k),r(k),zeta), tspan, y0);
end

figure
for k = 1:N
    subplot(N,1,k)
    plot(t,y{k})
    grid
    title(sprintf('f = %.1f, r = %.1f',f(k),r(k)))
    legend('$\dot{y_2}$','$y_2$', 'Interpreter','latex', 'Location','bestoutside')
end

function dydt= odefcn(t,y,f,r,zeta)
dydt=zeros(2,1);
dydt(1)=y(2);
dydt(2)=f.*sin(r*t)-2.\zeta.*y(2)-sin(y(1));
end

The code runs without error, however ‘odefcn’ needs to be carefully edited to be certain it is correct.

.

Answer 2

[Image Analyst]

There is no zeroeth element like you try to assign here:

y(0)=0.5;

The first index is 1, not 0.

This is not valid syntax:

dy/dt(0)=0;

not sure what you were thinking there but you might be able to delete the whole line.

This seems to be missing a command and left bracket and maybe some other stuff

options = odeset('RelTol',1e-6,'AbsTol' 1e-9 1e-9]);

Like maybe it should be:

options = odeset('RelTol', 1e-6, 'AbsTol',  [1e-9, 1e-9]);

That's a start anyway. Fix those and then there may be other errors but just work your way through them one at a time.