Subplot for individual for loop angle

I am trying to do subplot for each angle like the one below. But when I try to do it it only show the sine wave for all the angle on subplot(2,2,1).

Below is my code

for angle = [0.2 , deg2rad(7.5), deg2rad(30), deg2rad(45)]

for i=1

subplot(2,2,i)

%theta(0) = 0.2 rad

initial_x = [angle;0];

[t,x] = ode45(@fun, t, initial_x);

%figure

hold on

%graph for 0.2 rad of Part A (Non-Linear), plotted in red

plot(t,x(:,2))

%theta(0) = 0.2 rad

initial_y1 = [angle;0];

[t,y] = ode45(@fun1, t, initial_y1);

%graph for 0.2 rad of Part B (Linear), plotted in blue

plot(t,y(:,2))

grid on

title("Angular Velocity VS Time (" +angle+ " rad)")

xlabel('Time (s)')

ylabel('Angular Velocity (\omega)')

legend('Part A (Non-Linear)','Part B (Linear)')

hold off

end

end

[Star Strider]

The plots appear to me to be correct.

What is the exact problem? (Also, if solving it requires ‘fun’ and ‘fun1’ they need to be posted.)

.

[Jun Hong Wang]

My bad should have clarify that the above graph is the graph I want to make but with the current code I have I can only get the result below. I have also included who whole code

close all
clear
    
%Graph for velocity against time
%0.1 rad, 0.13 rad, 0.52 rad, 0.79 rad are plotted together

global g l
g = 9.81; %gravity
l = 9.81; %length
dt = 0.001; %time interval
t = 0:dt:10; %time from 0 to 10



    
for angle = [0.2 , deg2rad(7.5), deg2rad(30), deg2rad(45)]
for i=1
    subplot(2,2,i)

%theta(0) = 0.2 rad
initial_x = [angle;0]; 
[t,x] = ode45(@fun, t, initial_x);
%figure

hold on
%graph for 0.2 rad of Part A (Non-Linear), plotted in red
plot(t,x(:,2))  
             
%theta(0) = 0.2 rad
initial_y1 = [angle;0]; 
[t,y] = ode45(@fun1, t, initial_y1);           
%graph for 0.2 rad of Part B (Linear), plotted in blue
plot(t,y(:,2))     
grid on
title(sprintf('Angular Velocity VS Time (%.2f rad)', angle));
xlabel('Time (s)')
ylabel('Angular Velocity (\omega)')
legend('Part A (Non-Linear)','Part B (Linear)')
hold off
end
end


            

                
function dxdt = fun(~,x) %Non-linear function (Part A)
    global g l
    dx1dt = x(2);
    dx2dt = -(g/l)*sin(x(1));
    dxdt = [dx1dt;dx2dt];
end

function dydt = fun1(~,y) %Linear function (Part B)
    global g l
    dy1dt = y(2);
    dy2dt = -(g/l)*(y(1));
    dydt = [dy1dt;dy2dt];
end

Answer 1

[Drishan Poovaya]

Hi,

the reason the graph isn't being plotted the way you expect is because your nested for loop structure is incorrect for this case. You want 4 plots on different subplots. Refer to the code below. It is identical to your code but I've modified the for loops. Only one for loop is required for plotting, and a variable i is used to select the different subplots

close all
clear

%Graph for velocity against time
%0.1 rad, 0.13 rad, 0.52 rad, 0.79 rad are plotted together
global g l
g = 9.81; %gravity
l = 9.81; %length
dt = 0.001; %time interval
t = 0:dt:10; %time from 0 to 10
%start at subplot 2,2,1
i = 1;
for angle = [0.2 , deg2rad(7.5), deg2rad(30), deg2rad(45)]
    
    subplot(2,2,i);
    % increment i, so next plot is on next subplot and so on
    i = i+1;
    %theta(0) = 0.2 rad
    initial_x = [angle;0];
    [t,x] = ode45(@fun, t, initial_x);
    %figure
    hold on
    %graph for 0.2 rad of Part A (Non-Linear), plotted in red
    plot(t,x(:,2))
    
    %theta(0) = 0.2 rad
    initial_y1 = [angle;0];
    [t,y] = ode45(@fun1, t, initial_y1);
    %graph for 0.2 rad of Part B (Linear), plotted in blue
    plot(t,y(:,2))
    grid on
    title(sprintf('Angular Velocity VS Time (%.2f rad)', angle));
    xlabel('Time (s)')
    ylabel('Angular Velocity (\omega)')
    legend('Part A (Non-Linear)','Part B (Linear)')
    hold off
end


function dxdt = fun(~,x) %Non-linear function (Part A)
global g l
dx1dt = x(2);
dx2dt = -(g/l)*sin(x(1));
dxdt = [dx1dt;dx2dt];
end
function dydt = fun1(~,y) %Linear function (Part B)
global g l
dy1dt = y(2);
dy2dt = -(g/l)*(y(1));
dydt = [dy1dt;dy2dt];
end

[Jun Hong Wang]

Thank you so much! Really appreciate it.