Subscripted assignment dimension mismatch error in kinematic analysis of a 1 DOF mechanism

Greetings.

I have been trying to analyze a 1DOF mechanism by Newton Raphson algorythm but I always get the "Subscripted assignment dimension mismatch." error in line 59. How can I solve this? Thank you for your answers. The whole code is below:

clc,
clear,

% Input - defining physical parameters of mechanism
a2=31;a3=64;a4=35;
% Maximum Iteration
Nmax=100;
% Input - defining initial guess values for th3,th4,tau,s
x=[205*pi/180,66*pi/180,76,57];
% Error Tolerance
xe=0.001*abs(x);
% Input - System inputs (th2, w2, al2)
dth=5*pi/180;
th2=0*pi/180:dth:180*pi/180;
w2=10*ones(1,length(th2));
al2=0*ones(1,length(th2));
%--------------
xe=transpose(abs(xe));
kerr=1;     %if kerr=1, results won't be converged

for k=1:1:length(th2);
    for n=1:Nmax;
        % Assign initial guess values
        th3(k)=x(1);th4(k)=x(2);tau(k)=x(3);s(k)=x(4);
        % Input - Jacobian Matrix
        J=zeros(4,4);
        J(1,2)=-a4*sin(th4(k));
        J(2,2)=a4*cos(th4(k));J(2,3)=-1;
        J(3,1)=-a3*sin(th3(k));J(3,4)=1;
        J(4,1)=a3*cos(th3(k));
        % Input - f vectors
        f=zeros(4,1);
        f(1,1)=-(a2*cos(th2(k))+a4*cos(th4(k))+4);
        f(2,1)=-(a2*sin(th2(k))+a4*sin(th4(k))-s);
        f(3,1)=-(a2*cos(th2(k))+a3*cos(th3(k))+tau);
        f(4,1)=-(a2*sin(th2(k))+a3*sin(th3(k)));
        %-----------------
        eps=inv(J)*f;x=x+transpose(eps);
        if abs(eps)<xe;
            kerr=0;break
        end
    end
    if kerr==1;
        'Error nr';
    end
    th3(k)=x(1);th4(k)=x(2);
    tau5(k)=x(3);tau6(k)=x(4);

    % Velocity analysis
    fv(1,1)=w2(k)*a2*sin(th2(k));
    fv(2,1)=-w2(k)*a2*cos(th2(k));
    fv(3,1)=w2(k)*a2*sin(th2(k));
    fv(4,1)=-w2(k)*a2*cos(th2(k));
    vel=inv(J)*fv;
    w3(k)=vel(1);w4(k)=vel(2); 
    Vtau(k)=vel(3);Vs(k)=vel(4);
    
    %Acceleration analysis
    fa(1,1)=al2*a2*sin(th2(k))+w2.^2+a2*cos(th2(k))+w4.^2*a4*cos(th4(k));
    fa(2,1)=-al2*a2*cos(th2(k))+w2.^2*a2*sin(th2(k))+w4.^2*a4*sin(th4(k));
    fa(3,1)=al2*a2*sin(th2(k))+w2.^2*a2*cos(th2(k))+w3.^2*a3*cos(th3(k));
    fa(4,1)=-al2*a2*cos(th2(k))+w2.^2*a2*sin(th2(k))+w3.^2*a3*sin(th3(k));
    acc=inv(J)*fa;
    al3=acc(1);al4=acc(2);atau=acc(3);as=acc(4);
end

% Angle: Radian to degree
th2d=th2*180/pi;
th3d=th3*180/pi;
th4d=th4*180/pi;

% Plots
figure(1),
subplot(4,3,1),plot(th2d,th3d,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\theta_3 (^o)'),xlim([0 180])
subplot(4,3,2),plot(th2d,w3,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\omega_3 (r/s)'),xlim([0 180])
subplot(4,3,3),plot(th2d,al3,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\alpha_3 (r/s^2)'),xlim([0 180])

subplot(4,3,4),plot(th2d,th4d,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\theta_4 (^o)'),xlim([0 180])
subplot(4,3,5),plot(th2d,w4,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\omega_4 (r/s)'),xlim([0 180])
subplot(4,3,6),plot(th2d,al4,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\alpha_4 (r/s^2)'),xlim([0 180])

subplot(4,3,7),plot(th2d,tau,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\tau_5 (cm)'),xlim([0 180])
subplot(4,3,8),plot(th2d,Vtau,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\v tau_5 (cm/s)'),xlim([0 180])
subplot(4,3,9),plot(th2d,atau,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\a tau_5 (cm/s^2)'),xlim([0 180])

subplot(4,3,10),plot(th2d,s,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\tau_6 (cm)'),xlim([0 180])
subplot(4,3,11),plot(th2d,Vs,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\v tau_6 (cm/s)'),xlim([0 180])
subplot(4,3,12),plot(th2d,as,'r','linewidth',2),xlabel('\theta_2 (^o)'),ylabel('\a tau_6 (cm/s^2)'),xlim([0 180])

Answer 1

[Vimal Rathod]

You could try initializing fa varible with zeros using "zeros function" before assigning it to the above expression in your code. I think that would remove the dimension mismatch error you are getting.

Try debugging your code and find out the size of Right hand side expression. Then initializing variable fa with proper size would solve your error.

[Zafer Duyenli]

Okay I found out that I didn't initialize the variable such as w2, al2, etc in iterations. I should have inputted them in form of w2(k), al2(k), etc.

Thank you so much!