Creating a video giving oscillatory motion to a point

How do I create a video having a single point (or a solid circle) moving in a oscillatory motion with a predefined frequency and amplitude?

[KALYAN ACHARJYA]

Is it animate?

[Soumya Kedia]

Yes. Basically I just want any object to be having to and fro motion with a fixed frequency and amplitude.

Answer 1

[KSSV]

A = 0.5 ; 
f = 1 ; 
t = linspace(0,10,100) ; 
 
x = A*sin(2*pi*f*t) ; 
h = plot(0.,x(1),'s','MarkerSize',10) ; 
for i = 1:length(x)
  set(h,'YData',x(i)) ; 
  drawnow
end

If you want more, you may refer:

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

https://in.mathworks.com/matlabcentral/fileexchange/33168-springpendulum

[Soumya Kedia]

Thank you so much. This is exactly what I needed.

[Soumya Kedia]

I have added few lines to help me save the video. The problem is, for each frame, the y axis keeps changing and I'm unable to fix it, and hence my video is not proper.

Can you help with that?

Here is the code that I'm using now.

A = 0.5 ; 
f = 1 ; 
t = linspace(0,1,100) ; 
 
x = A*sin(2*pi*f*t) ; 
h = plot(0,x(1),'o','MarkerSize',10) ; 
xlim([-1 1]);

%% Initialize video
myVideo = VideoWriter('myVideoFile'); %open video file
myVideo.FrameRate = 10;  %can adjust this, 5 - 10 works well for me
open(myVideo)
for i = 1:length(x)
  set(h,'YData',x(i)) ;
  pause(0.01) %Pause and grab frame
  frame = getframe; %get frame
  writeVideo(myVideo, frame);
end

close(myVideo)

Answer 2

[KALYAN ACHARJYA]

Here is the MATLAB File Exchange File for Pendulum Link

Credit:Sathyanarayan Rao

The oscillatory motion of a simple pendulum is simulated using Euler-Cromer method.

I have remove the energy calculation part, hope you can change change the amplitude and frequency of the pendulum.

%-------------------------------------------------------------------------
%---Simple pendulum using Euler-Cromer Numerical Method------------------
%Credit:Sathyanarayan Rao
%------------------------------------------------------------------------
clc;
clear all;
close all;
L= 1;  % Length of Pendulum
g=9.8; % Gravity 
M=1; % mass
N=300;  % Maximum number of time steps
dt=0.01;  % Step size for time
w(1:N)=0;  % Angular velocity array
Theta(1:N)=0;  % Angular coordinate array
t(1:N)=0;   % Time array
Theta(1)=0.5; % Initial position of pendulum
for i=1:N-1
    w(i+1)=w(i)-(g/L)*Theta(i)*dt;
    Theta(i+1)=Theta(i)+w(i+1)*dt;
    X(i)=L*sin(Theta(i)); % polar to cartesian
    Y(i)=-L*cos(Theta(i));
    t(i+1)=t(i)+dt;
end
  
for i=1:N
    figure(1)
    plot(X(i),Y(i),'.','markersize',65); 
    axis([-0.5 0.5  -1.05 0]);
    line([0 X(i)], [0 Y(i)],'Linewidth',2);
    xlabel('X '); 
    ylabel('Y'); 
    titlestring = ['pendulum motion at t =',num2str(i*dt), 'seconds'];
    title(titlestring ,'fontsize',14);                            
    h=gca; 
    get(h,'FontSize') ;
    set(h,'FontSize',14);
    fh = figure(1);
    set(fh, 'color', 'white'); 
    Yr=getframe;
end
 movie(Yr)

[Soumya Kedia]

Thank you, the code works, but I just needed a point in a straight line going to and fro, since I need that to ckeck another one of my code and i need to find the motion of the centroid to check it's oscillatory. I'll see if I can make changes in this, or get an idea from this one to get what I want.