Equation of motion of Non linear pendulum

tspan=[0,2*pi];
u0=[pi/4;0];
[t,u]=ode45(@pendulum,tspan,u0,[]);
plot(t,u(:,1),'b-', 'LineWidth', 2)
xlabel('time')
ylabel('angle')

function zdot = pend (t,z)  
wsq = 1.56; % specify a value of w"2
t = time;
z = [z (l) ; z ( 2)] = [theta; thetadot] 
zdot = [z (2) ; -wsq* sin (z(l))]; 
end

This doesn't seem to be working. I'm trying to plot the discplacement versus time and velocity versus time. Any idea as to what the problem mightbe?

I got this from Rudra pratap. I've attached a link to the book, it's on page 159 (173 by docs)

https://lpuguidecom.files.wordpress.com/2017/05/p1-11385-scripts-and-matrix-operations.pdf

[KLETECH MOTORSPORTS]

( Second Order non linear ODE )

[KSSV]

Refer this: https://in.mathworks.com/matlabcentral/fileexchange/33082-simplependulum

Answer 1

[Bjorn Gustavsson]

Note that the function you use for the input-argument to ode45 is pendulum while the function you implemented for the pendulum has the name pend. They should be the same. When that's fixed there seems to be no major problems with your code:

u0=[pi/4;0];
pend = @(t,z) [z(2);-1.56*sin(z(1))];
figure
tspan=[0,12*pi]; % just a slightly longer time-span
[t,u]=ode45(pend,tspan,u0,[]);
plot(t,u)

HTH

[KLETECH MOTORSPORTS]

[KLETECH MOTORSPORTS]

i got this error

[Bjorn Gustavsson]

Ok, that is because your script is named pend.m and then matlab doesn't like the naming-confusion with a variable with that name in the script. You should be fine if you rename the variable to someting like pendODE for example.

HTH