How to Plot the Trajectory of a Point

I am trying to plot the trajectory of P4 as it travels in the animation.

hold on

axis equal
axis off

b = 0:pi/60:pi/6;
c = 0:pi/30:pi/3;
d = 0:pi/20:pi/2;

for k = 1:numel(b)
    P1=[-15,0];
    P2=[-5,0];
    plot([P1(1) P2(1)],[P1(2) P2(2)],'LineWidth',5,'Color','black');
    
    A=[0,0];
    h{1} = viscircles(A,5,'LineWidth',2,'Color','black'); 
    
    B = A+[10*cos(b(k)-pi/6),10*sin(b(k)-pi/6)];
    h{2} = viscircles(B,5,'LineWidth',2,'Color','green');
    
    C = B+[10*cos(c(k)-pi/3),10*sin(c(k)-pi/3)];
    h{3} = viscircles(C,5,'LineWidth',2,'Color','blue');
    
    D = C+[10*cos(d(k)-pi/2),10*sin(d(k)-pi/2)];
    h{4} = viscircles(D,5,'LineWidth',2,'Color','red');
    
    P3=D+[5*cos(d(k)-(pi/2)),5*sin(d(k)-(pi/2))];
    P4=D+[15*cos(d(k)-(pi/2)),15*sin(d(k)-(pi/2))];
    h{5} = plot([P3(1) P4(1)],[P3(2) P4(2)],'LineWidth',5,'Color','black');
    
    drawnow();
    pause(0.5);
    delete( vertcat(h{:}) );
end
hold off
axis equal
axis off

Answer 1

[Star Strider]

Experiment with this:

P4vct = nan(numel(b),2);                    % Preallocate Before The ‘n’ Loop

then add these two lines after your ‘h{5}’ assignment:

P4vct(k,:) = P4;
h{6} = plot(P4vct(:,1),P4vct(:,2), '--','LineWidth',5,'Color','black');

It will then plot (what I believe to be) the ‘P4’ trajectory as a dashed black line.

That should at least give you an idea of the approach.