Error using sym/subsindex , Error in sym/subsref

syms Ybus k n V i N;
V(k,i) = (1/Ybus(k,k))*((conj(S(k)))/(conj(V(k,i)))-(symsum(Ybus(k,n)*V(n,i+1),n,1,k-1)) -(symsum(Ybus(k,N)*V(N,i),n,k+1,N))); 


Error using sym/subsindex (line 855)
Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic variables, and function body must be sym
expression.

Error in sym/subsref (line 900)
            R_tilde = builtin('subsref',L_tilde,Idx);

Error in hmw (line 28)
V(k,i) = (1/Ybus(k,k))*((conj(S(k)))/(conj(V(k,i)))-(symsum(Ybus(k,n)*V(n,i+1),n,1,k-1)) -(symsum(Ybus(k,N)*V(N,i),n,k+1,N)));

Where is the problem ?

Answer 1

[Ameer Hamza]

You are using Ybus, S, and V as functions, however, you defined them as simple symbolic variables. Try this

syms Ybus(k,n) V(k,i) N S(k)
V(k,i) = (1/Ybus(k,k))*((conj(S(k)))/(conj(V(k,i)))-(symsum(Ybus(k,n)*V(n,i+1),n,1,k-1)) -(symsum(Ybus(k,N)*V(N,i),n,k+1,N))); 

Also, here you are defining V(k,i) in terms of V(k,1). It appears there might be a logical error. Can you show the equation you are trying to implement?