Variable size is incorrect

%% Calculations for a 4 bar linkage
% Orgin
Ox=0;
Oy=0;

%% Link Lengths
L1=6;
L2=2;
L3=7;
L4=9;
x_size=1
theta2=30;

%% K values
for i = 1:x_size
  
     K1= L1(i)/L2(i);
     K2= L1(i)/L4(i);
     K3= (L2(i)^2-L3(i)^2+L4(i)^2+L1(i)^2)/(2*L2(i)*L4(i));
     K4= L1(i)/L3(i);
     K5= (L4(i)^2-L3(i)^2-L2(i)^2-L1(i)^2)/(2*L2(i)*L3(i));
end
%% Calculate OTHER variables here.

   a= cosd(theta2)-K1-K2*cosd(theta2)+K3;
     b= -2*sind(theta2);
     c= K1-(K2+1)*cosd(theta2)+K3;
     d= cosd(theta2)-K1+K4*cosd(theta2)+K5;
     e= -2*sind(theta2);
     f= K1+(K4-1)*cosd(theta2)+K5;






%% Calculate your thetas   
for i=1:1:361
         theta4(i)= 2*atand((-b-(b^2-4*a*c)^(1/2))/(2*a));
         theta3(i)= 2*atand((-e-(e^2-4*d*f)^(1/2))/(2*d));
end
    
%% Determine the ABSOLUT position of the ENDS of each link (for plotting)

  L2X =L2*cos(theta2)
    L2Y =L2*sin(theta2)

    L3X =L3*cos(theta2)
    L3Y =L3*sin(theta2)

    L4X =L4*cos(theta2)
    L4Y =L4*sin(theta2)

    RPX =L2X+L3X
    RPY =L2Y+L3Y

%% Plot variables    
line_width = 4.5;
marker_size = 9;

%% WHAT INDEX VALUE SHOULD THIS BE IF YOU WANT TO PLOT theta2 = 45 degrees?  
ii = 1 % CHANGE THIS NUMBER BUT USE IT TO CREATE THE CORRECT PLOT POSITION AS REQUIRED 


figure(1)
hold on
plot([0 L2X],[0 L2Y],'-^k') % Plot the ground link as black with triangles at each end. Change the line width and markersize so the the link is visible
plot([0 L3X],[0 L3Y],'-or') % Plot the crank link as red with circles at each end. Change the line width and markersize so the the link is visible
plot([0 L4X],[0 L4Y],'-og') % Plot the coupler link as green with circles at each end. Change the line width and markersize so the the link is visible
plot([0 RPX],[0 RPY],'-ob') % Plot the output link as blue with circles at each end. Change the line width and markersize so the the link is visible

I keep getting this error and Im not sure how to fix it