How to Create a matching x vector for plot

Please look at the following code. I want to plot y vs. x. However I get the following error:

Error using plot. Vectors must be the same length. Error in orbitthreebody (line 12) plot(x,y)

I know that y is correct. How do I create a matching x vector so that I can make my plot?

function z=orbitthreebody(inter,ic,n,p)
h=(inter(2)-inter(1))/n;        % plot n points 
x1=ic(1);vx1=ic(2);y1=ic(3);vy1=ic(4);  % grab initial conds
x2=ic(5);vx2=ic(6);y2=ic(7);vy2=ic(8);
x3=ic(9);vx3=ic(10);y3=ic(11);vy3=ic(12);

y(1,:)=[x1 vx1 y1 vy1 x2 vx2 y2 vy2 x3 vx3 y3 vy3];t(1)=inter(1);    % build y vector
set(gca,'XLim',[-5 5],'YLim',[-5 5],'XTick',[-5 0 5],'YTick',[-5 0 5]);

x = linspace(0,12);
plot(x,y)

for k=1:n/p
  for i=1:p
    t(i+1)=t(i)+h;
    y(i+1,:)=trapstep(t(i),y(i,:),h);
  end
  
  y(1,:)=y(p+1,:);t(1)=t(p+1);
  clearpoints(head1);clearpoints(head2);clearpoints(head3);
  addpoints(head1,y(1,1),y(1,3))
  addpoints(tail1,y(1,1),y(1,3))
  addpoints(head2,y(1,5),y(1,7))
  addpoints(tail2,y(1,5),y(1,7))
  addpoints(head3,y(1,9),y(1,11))
  addpoints(tail3,y(1,9),y(1,12))
  
  drawnow;
  a=3;
  axis([-a a -a a -a a])
  frame=getframe;writeVideo(v,frame);
  
end
close(v)

function y=eulerstep(t,x,h)
y=x+h*ydot(t,x);

function y = trapstep(t,x,h)
z1=ydot(t,x);
g=x+h*z1;
z2=ydot(t+h,g);
y=x+h*(z1+z2)/2;

function z = ydot(t,x)
m1=0.03;
m2=0.3;
m3=0.03;

g=1;mg1=m1*g;mg2=m2*g;mg3=m3*g;

px1=x(1);py1=x(3);pz1=x(5);vx1=x(2);vy1=x(4);vz1=x(6);
px2=x(7);py2=x(9);pz2=x(11);vx2=x(8);vy2=x(10);vz2=x(12);
px3=x(13);py3=x(15);pz3=x(17);vx3=x(14);vy3=x(16);vz3=x(18);

dist12=sqrt((px2-px1)^2+(py2-py1)^2+(pz2-pz1)^2);
dist23=sqrt((px2-px3)^2+(py2-py3)^2+(pz2-pz3)^2);
dist13=sqrt((px1-px3)^2+(py1-py3)^2+(pz1-pz3)^2);

z=zeros(1,12);
z(1)=vx1;
z(2)=(mg2*(px2-px1))/(dist12^3)+(mg3*(px3-px1))/(dist13^3);
z(3)=vy1;
z(4)=(mg2*(py2-py1))/(dist12^3)+(mg3*(py3-py1))/(dist13^3);
z(5)=vx2;
z(6)=(mg1*(px1-px2))/(dist12^3)+(mg3*(px3-px2))/(dist23^3);
z(7)=vy2;
z(8)=(mg1*(py1-py2))/(dist12^3)+(mg3*(py3-py2))/(dist23^3);
z(9)=vx3;
z(10)=(mg1*(px1-px3))/(dist13^3)+(mg2*(px2-px3))/(dist23^3);
z(11)=vy3;
z(12)=(mg1*(py1-py3))/(dist13^3)+(mg2*(py2-py3))/(dist23^3);

Answer 1

[Star Strider]

I can’t run the code because I have no idea what the arguments are.

That aside, try this —

x = linspace(0,12,numel(y));
plot(x,y)

That should equalise the lengths, and the plot should work.

I have no idea if it solves any other problems that could be present in the code.

.