i try to put two plot in one graph using legend but one of them just looks been 'cut off', can someone help me to fix this problem

x0=2.1;
g=9.81;
k=45;
m=7;
t=0:0.1:6;
x1=@(t) x0*cosd(t*(sqrt(k/m)));
x_t_undamped=x1(t);
%ii
figure
plot(x_t_undamped,t,'-b');
xlabel('Position(m)');
ylabel('Time (s)');
title('Position of mass vs time');
hold on
%b
%i%ii%iii
dA=23;
v0=0;
A = dA / (2 * m);
B = sqrt(k / m - (dA/2*m)^2);
C2 = x0;
C1 = C2*B/ A;
x2 = @(t) exp(-A * t) .* (C1 * sind(B* t) + C2 * cosd(B* t));
x_t_underdamped=x2(t);
plot(t,x_t_underdamped, 'r-'); 
legend('undamped','underdamped')
grid on7
fprintf('The system is underdamped because the damping ratio is greater than 1.\n');

[Sam Chak]

Although the answers showed to you how to correctly plot the result, you should review whether to use sind for degree, or sin() for radian.

Answer 1

[Alan Stevens]

Plot both curves the same way (i.e. t then x)!

x0=2.1;
g=9.81;
k=45;
m=7;
t=0:0.1:6;
x1=@(t) x0*cosd(t*(sqrt(k/m)));
x_t_undamped=x1(t);
%ii
subplot(2,1,1)
plot(t,x_t_undamped,'-b');
xlabel('Time(s)');
ylabel('Position (m)');
grid
title('Position of mass vs time undamped');

%b
%i%ii%iii
dA=23;
v0=0;
A = dA / (2 * m);
B = sqrt(k / m - (dA/2*m)^2);
C2 = x0;
C1 = C2*B/ A;
x2 = @(t) exp(-A * t) .* (C1 * sind(B* t) + C2 * cosd(B* t));
x_t_underdamped=x2(t);
subplot(2,1,2)
plot(t,x_t_underdamped, 'r-'); 
xlabel('Time(s)');
ylabel('Position (m)');
grid
title('Position of mass vs time underdamped');

fprintf('The system is underdamped because the damping ratio is greater than 1.\n');

The system is underdamped because the damping ratio is greater than 1.

Answer 2

[Shivam Gothi]

Hello @Elisa,

According to my understanding, you are trying to plot responses of underdamped and undamped system on same graph.

I went through your code and found that following changes are needed to be made

1) There is a typing mistake in the below given line of code:

    plot(x_t_undamped,t,'-b');

The time variable "t" should be on x-axis and "x_t_undamped" on y-axis. Therefore, change the line of code to:

    plot(t,x_t_undamped,'-b');

2) Increase the time span of plot

consider the below given line of your code.

    t=0:0.1:6;

Change it to the line as shown below:

    t=0:0.1:200;

Run the script again, you will now get a plot as shown below:

I hope this is what you expected.

[Sam Chak]

Note that the labels on the axes should be swapped, for proper display of info.

[Shivam Gothi]

Thanks Sam Chak for pointing it out. I edited it.

[Sam Chak]

Hi Shivam, you can actually copy/paste the code and run it online in the forum.