error index exceeds matrix dimension. I am not using matrix

syms th d alpha a th1 th2 l1 l2 lc1 lc2 I1z I2z m1 m2
d(1,1)=m1*lc1^2+m2*(l1^2+lc2^2+2*lc2*l1*cos(th2))+I1z+I2z;
d(1,2)=m2*(lc2^2+l1*lc2*cos(th2))+I2z;
diff(d(1,2),th(1))+diff(d(1,1),th(2))

Index exceeds matrix dimensions.

Answer 1

[KSSV]

   syms th d alpha a th1 th2 l1 l2 lc1 lc2 I1z I2z m1 m2
  d(1,1)=m1*lc1^2+m2*(l1^2+lc2^2+2*lc2*l1*cos(th2))+I1z+I2z;
  d(1,2)=m2*(lc2^2+l1*lc2*cos(th2))+I2z;
  diff(d(1,2),th1)+diff(d(1,1),th2)

It should be th1 and th2 not th(1), th(2)

[Muhammad Salahul Din]

syms th d alpha a th1 th2 l1 l2 lc1 lc2 I1x I1y I2x I2y I1z I2z m1 m2 Gamma

D=[m1*lc1^2+m2*(l1^2+lc2^2+2*lc2*l1*cos(th2))+I1z+I2z m2*(lc2^2+l1*lc2*cos(th2))+I2z; m2*(lc2^2+l1*lc2*cos(th2))+I2z m2*(lc2^2)+I2z];

d(1,1)=D(1,1); d(1,2)=D(1,2); d(2,1)=D(2,1); d(2,2)=D(2,2);

n=2;

for gamma = 1:n
  for beta = 1:n
    for alpha = 1:n
       Gamma (gamma, beta, alpha) = 0.5 * ... 
          (diff (d(alpha, beta),  th(gamma)) + ...           
           diff (d(alpha, gamma), th(beta))  - ...
           diff (d(gamma, beta),  th(alpha)));
    end
  end
end
Gamma (:, :, gamma)

%Can you correct that please. This code is not working.

[Muhammad Salahul Din]

I am trying to find out christoffel symbols

[Sunny Katyara]

Dear Muhammad Salahul Din, did you find the christoffel symbols? Can you share the code here Please?