how to combine two plots in one figure

I have the following code and would like to plot the motion of a particle under the influence of magnetic field with two intensity It should look something like this:

But for some reason my code doesn't show the right sizes:

dt = 1e-2; % time step
mass = 1.0; % mass of particle 
charge = 1.0; % charge of particle
n = 500; % number of time steps

%Initial parameters:
v = [0, 1, 0]; % initial velocity
x = [0, 0, 0]; % initial position 

B1 = [0, 0, 10];%B = [0, 0, 10]; initial mag. field along z directions
B2 = [0, 0, 2];
E = [0, 0, 0]; % initial E field, for case 1) E = 0 and B =/ 0

X = zeros(n,3); % initialize an array of zeros with size nx3 for positions
V = zeros(n,3); 

X1 = zeros(n,3); % initialize an array of zeros with size nx3 for positions
V1 = zeros(n,3);
X2 = zeros(n,3); % initialize an array of zeros with size nx3 for positions
V2 = zeros(n,3);
for time = 1:1:n
    [x1,v] = boris_rotation(x,v,charge,mass,dt,B1,E);
    [x2,v2] = boris_rotation(x,v,charge,mass,dt,B2,E);
    X1(time,:) = x1;
    V1(time,:) = v;
    X2(time,:) = x2;
    V2(time,:) = v2;
end
figure;
 plot(X1(:,1),X2(:,2),'k','Linewidth',2); 
 grid on
 hold on
 plot(X2(:,1),X1(:,2),'r','Linewidth',2);

I am getting this:

Answer 1

[Jakob B. Nielsen]

In your code, you input the initial x and v during every loop iteration - not the most recent x and v. That is why you just get two circles on top of each other.

This small change gives me a figure that looks, not quite like the first one you posted, but a whole lot closer, and you can work from there :)

x1=x;  %initial positions 'zeroed'
x2=x;
for time = 1:1:n
    [x1,v] = boris_rotation(x1,v,charge,mass,dt,B1,E); %input x1 instead of x
    [x2,v2] = boris_rotation(x2,v2,charge,mass,dt,B2,E); %input x2 instead of x, and also v2 instead of v
    X1(time,:) = x1;
    V1(time,:) = v;
    X2(time,:) = x2;
    V2(time,:) = v2;
end