Matlab plot3 not giving a 3D plot

Hi all, Sorry I'm a beginner with Matlab and don't understand why my plot3 with 3 inputs is not giving me a 3D representation of 4 bugs travelling on a 3D plane?

Here is my code:

clc, clear, clear all

ti=0;
tf=1000;
tspan= linspace(ti,tf,1000000);
f0 = [0; 0; 0; 1; 2; 0; 1; 0; 3; 0; 2; 3];
[t, f] = ode45(@g, tspan, f0);

%Trajectories are done in 3 coordinates x,y,z
i_1=(f(:,1)); %Trajectory of bug 1
j_1=(f(:,2));
k_1=(f(:,3));

i_2=(f(:,4)); %Trajectory of bug 2
j_2=(f(:,5));
k_2=(f(:,6));

i_3=(f(:,7)); %Trajectory of bug 3
j_3=(f(:,8));
k_3=(f(:,9));

i_4=(f(:,10));
j_4=(f(:,11));
k_4=(f(:,12));

figure
hold on
plot3(i_1, j_1, k_1)
plot3(i_2, j_2, k_2)
plot3(i_3, j_3, k_3)
plot3(i_4, j_4, k_4)
title('test')
xlabel('x')
ylabel('y')
zlabel('z')

function dxdt = g(t,f)
a = sqrt((f(2)-f(1))^2 + (f(6)-f(5))^2 + (f(10)-f(9))^2);
b = sqrt((f(3)-f(2))^2 + (f(7)-f(6))^2 + (f(11)-f(10))^2);
c = sqrt((f(4)-f(3))^2 + (f(8)-f(7))^2 + (f(12)-f(11))^2);
d = sqrt((f(1)-f(4))^2 + (f(5)-f(8))^2 + (f(9) -f(12))^2);

dxdt = [ ...
    (f(2)  - f(1))  / a;
    (f(6)  - f(5))  / a;
    (f(10) - f(9))  / a;
    (f(3)  - f(2))  / b;
    (f(7)  - f(6))  / b;
    (f(11) - f(10)) / b;
    (f(4)  - f(3))  / c;
    (f(8)  - f(7))  / c;
    (f(12) - f(11)) / c;
    (f(1)  - f(4))  / d;
    (f(5)  - f(8))  / d;
    (f(9)  - f(12)) / d];
end

Thank you

[Torsten]

Did you see the plots generated by plot3 under

https://de.mathworks.com/help/matlab/ref/plot3.html

?

Do you have a different expectation about the plot ?

[Jonas Freiheit]

Hi Torsten, when I run my plot3 I get this result in 2D...

[Torsten]

figure
plot3(i_1, j_1, k_1)
hold on
plot3(i_2, j_2, k_2)
hold on
plot3(i_3, j_3, k_3)
hold on
plot3(i_4, j_4, k_4)
title('test')
xlabel('x')
ylabel('y')
zlabel('z')

instead of

figure
hold on
plot3(i_1, j_1, k_1)
plot3(i_2, j_2, k_2)
plot3(i_3, j_3, k_3)
plot3(i_4, j_4, k_4)
title('test')
xlabel('x')
ylabel('y')
zlabel('z')

[Jonas Freiheit]

Thank you Torsten, how can I accept your answer?

Also how can I make the plot interactive where I can change the view with my mouse.

[Cris LaPierre]

I suggest one minor change to Torsten's code:

figure
plot3(i_1, j_1, k_1)
hold on
plot3(i_2, j_2, k_2)
plot3(i_3, j_3, k_3)
plot3(i_4, j_4, k_4)
hold off
title('test')
xlabel('x')
ylabel('y')
zlabel('z')

Use the Axes Toolbar to rotate the plot. See here for how to access it in a live script:

https://www.mathworks.com/help/matlab/matlab_prog/modify-output-figures.html

[Jonas Freiheit]

Thanks Cris

Answer 1

[Steven Lord]

Since no axes existed when you called hold on, MATLAB created one using the default 2-D view and "locked" that axes property in place. Locking certain axes properties in place, so MATLAB doesn't automatically change them, is one of the main purposes of the hold function. So when you called plot3 it would have changed the view but effectively hold said "You can't do that."

The code @Cris LaPierre posted called plot3 before hold so the axes that was "locked" used the 3-D view. You could also call view to manually change the view. hold prevents MATLAB from automatically changing properties, but it doesn't prevent you the user from manually changing them.

figure
hold on
plot3(1:10, 1:10, 1:10) % Uses the 2-D view
view(3) % Manually change it to be in 3-D view