I'm trying to animate both the plots in the 2 for loops simultaneously. But it's getting executed one after the other. Can anyone help me resolve this. I need to get this done. I'm attaching images of plots for your undertanding.

clear 
close all
clc

%========================Given Inputs ==============================

b = 0.1;
g = 9.81;
l = 1;
m = 1;

%==================== Initial Condition =======================

theta_0 = [0,3];

%==================== Time Points =============================

t_span = linspace(0,20,500);

%==================== Solve Ode ===============================


 [t,results] = ode45(@(t,theta) ode_func(theta,b,g,l,m),t_span,theta_0);
 
%============ plotting pendulum motion w.r.t time =============
figure(2)
a = results(:,1);
b = results(:,2);
for j = 1:length(t)  
    subplot(2,1,1)
    plot(t(1:j),a(1:j),'b','linewidth',2);
    hold on
    plot(t(1:j),b(1:j),'g','linewidth',2);
    axis([0 20 -4 4]);
    xlabel('Time')
    ylabel('Plot')
    title('Plot of Angular Velocity & Displacement w.r.t Time')
    legend({'Displacement','Angular Velocity'})
    pause(0.1);
    hold off
end
 %=================== Using For loop ===========================
figure(2)
hold on
 ct = 1;
 for i = 1:length(results(:,1))
    subplot(2,1,2)
     x0 = 0;        %initial 'x' co-ordinate of pendulum string
     y0 = 0;        %initial 'y' co-ordinate of pendulum string    
     
     x1 = 1*sin(results(i,1));   % 'x' co-ordinate where the bob is attached
     y1 = -1*cos(results(i,1));  % 'y' co-ordinate where the bob is attached
     
     plot([0 0],[-1.5 0.5]);
     hold on
     plot([-1,1],[0,0],'linewidth',3,'color','b');
     line([x0 x1],[y0 y1],'linewidth',3,'color','g'); %pendulum string plot
     hold on
     plot(x1,y1,'o','markers',20,'markerfacecolor','r'); %plotting bob of the pendulum
     axis([-1.5 1.5 -1.5 0.5]);
     pause(0.9);
     hold off
     M(ct) = getframe(gcf);
     ct = ct+1;

 end
 
 %=================== Syntax for Movie ==========================
    
     movie(M)
     videofile = VideoWriter('Pendulum_oscillation.avi','Uncompressed AVI');
     open(videofile)
     writeVideo(videofile,M)
     close(videofile)
       

Answer 1

[Cris LaPierre]

Code executes top down. If you want the plots to update together, you'll have to put the code inside the same for loop.

Don't put code that only needs to be run once inside the for loops. Better is to create the original plot, and then update the XData and YData with a for loop.

[Abhinandan Angadi]

Can you please be more specific. I tried doing that too, but I didn't get any figure window.

[Cris LaPierre]

We don't have all your code, so I can't test a working example with what you've shared, but see this answer, since the suggestion given there is the same.

You might also look into animatedline for animating the top plot.

[Abhinandan Angadi]

 function [dtheta_dt] = ode_func(theta,b,g,l,m)
       theta1 = theta(1);
       theta2 = theta(2);
       dtheta1_dt = theta2;
       dtheta2_dt = -(b/m*l)*theta2-(g/l)*sin(theta1);
       dtheta_dt = [dtheta1_dt;dtheta2_dt];
 end

The above is the script used to the function used in the program.

[Cris LaPierre]

I'm only adding code for creating the plots. You'll still need the rest of your code, but I removed it here for clarity.

%==================== Solve Ode ===============================

[t,results] = ode45(@(t,theta) ode_func(theta,b,g,l,m),t_span,theta_0);

%============ plotting pendulum motion w.r.t time =============
figure(2)
% Displacement/Velocity plot
ax1=subplot(2,1,1);
axis([0 20 -4 4]);
h1 = animatedline('Color','b',"LineWidth",2,"Parent",ax1);
h2 = animatedline('Color','g',"LineWidth",2,"Parent",ax1);

a = results(:,1);
b = results(:,2);

xlabel('Time')
ylabel('Plot')
title('Plot of Angular Velocity & Displacement w.r.t Time')
legend({'Displacement','Angular Velocity'})

% Pendulum plot
ax2=subplot(2,1,2);
axis([-1.5 1.5 -1.5 0.5]);
axis equal
xline(0);
hold on
plot(ax2,[-1,1],[0,0],'linewidth',3,'color','b');

x0 = 0;        %initial 'x' co-ordinate of pendulum string
y0 = 0;        %initial 'y' co-ordinate of pendulum string

x1 = 1*sin(results(:,1));   % 'x' co-ordinate where the bob is attached
y1 = -1*cos(results(:,1));  % 'y' co-ordinate where the bob is attached

l1=line(ax2,[x0 x1(1)],[y0 y1(1)],'linewidth',3,'color','g'); %pendulum string plot
p=plot(ax2,x1(1),y1(1),'o',"MarkerSize",20,"MarkerFaceColor",'r');
hold off

%============ Animate plots ============
for j = 1:length(t)
    % add points one at a time to dispacement/velocity plot
    addpoints(h1,t(j),a(j))
    addpoints(h2,t(j),b(j))

    % Add points one at a time to pendulum plot
    p.XData=x1(j);
    p.YData=y1(j);
    % Animate the string
    l1.XData = [x0 x1(j)];
    l1.YData = [y0 y1(j)];
    drawnow
end

[Abhinandan Angadi]

Thanks a lot. Its working fine.

[Abhinandan Angadi]

The trace of the pendulum bob is overlapping, which is inappropriate. I' m not able to figure out why.

[Cris LaPierre]

Look at what code you are using to animate the pendulum. Are you adding more points, or are you updating the existing X and Y values?