Implement a particular equation

Hello everyone ,

I am trying to use matlab where I have to implement a equation which is mentioned below; I tried to implement it but where

I got error saysing:
Error using  + 
Matrix dimensions must agree.

Error in test181118 (line 42)
    K = prev_S*M'*(((W+M*S*M'))^-1);

My code:

S = [100 0 0 0 0 0;
    0 100 0 0 0 0;
    0 0 100 0 0 0;
    0 0 0 100 0 0;
    0 0 0 0 100 0;
    0 0 0 0 0 100];

prev_S = S;
a=0;
b=0;
c=0;
p=0;
q=0;
s=0;

est_vec=[a ; b; c; p; q; s];

Big_lambda=[1 0 0;
    0 1 0;
    0 0 1];
theta = [45 60 90 ] ;

t= [ 10 20 30 ];
     
r= [ 10 20 30];

x = [ r; theta ; t];
for i=1:3
     dif_x = [(-cos(theta(i))) (r(i).*sin(theta(i))) (2*a.*t(i)+b);(-sin(theta(i))) (-r(i).*cos(theta(i))) (2*p.*t(i)+q)];    
     
     W = dif_x(i).*Big_lambda.*dif_x(i)';
     
     
    M = [t(i).^2 t(i) 1 0 0 0;
         0 0 0 t(i).^2 t(i) 1];
 K = prev_S*M'*(((W + M*prev_S*M'))^-1);
 S = prev_S;
end

I am giving you dimension of the vectors and matrix:

prev_S = (6*6)
M = (2*6)
W = (3*3)

[Stephen23]

Here are the two terms that you are trying to add:

>> W
W =
   0.27596   0.00000   0.00000
   0.00000   0.27596   0.00000
   0.00000   0.00000   0.27596
>> M*prev_S*M'
ans =
   1010100         0
         0   1010100
         

How do you expect to add the elements of a 3x3 matrix and a 2x2 matrix?

More concretely, what does W(3,3) get added to? Once you can answer this question, then we can help you to fix your buggy code.