How to carry an unknown variable through computation and solve?

I am trying to carry an unknown variable through a couple steps of computation and solve for the unknown. I have written a "dummy" code to test my approach, and it works:

syms x
SS = cell(1,3)
G = 1;
DS = [0 1 2; 3 4 5; 6 7 8];
for n = 1:1
    SS{n} = [n n n; n n n; n n n];
    SSTSC = SS{n}+ x* DS;
   DDS = 0
    for i = 1:3
        for j = 1:3
            DDS = DDS + SSTSC(i,j)*SSTSC(i,j)
        end
    end
    eqn = (1/2)*DDS -(1/3)*G == 0
    solx = solve(eqn,x)
end

However, when I try to apply this approach to my code:

        syms x
        %mean of the trial stress tensor
        MDS = (DSTST{k}(1) + DSTST{k}(2) + DSTST{k}(3))/3; 
        %deviator of the trail stress tensor
        DS = [0 DSTST{k}(4)-MDS DSTST{k}(6)-MDS;
            DSTST{k}(4)-MDS 0 DSTST{k}(5)-MDS;
            DSTST{k}(6)-MDS DSTST{k}(5)-MDS 0]

        %Deviatoric Stress Tensor for contact stress state
        SC = S{k}+ x* DS

        %Compute S*S for contract stress state
        SSC = 0;
          for i=1:3        
              for j=1:3
                  SSC = SSC+ SC(i,j)*SC(i,j)
              end
          end    

         eqn =(1/2)*SSC-(1/3)*SIG{k} == 0
         R = solve(eqn,x)

I am getting error:

Error using assignin
Attempt to add "x" to a static workspace.
 See MATLAB Programming, Restrictions on Assigning to
 Variables for details.

Error in syms (line 66)
        assignin('caller',x,sym(x));

Error in J2FlowTheory (line 119)
        syms x

Answer 1

[Walter Roberson]

Replace the

syms x

with

x = sym('x');

or remove the "end" that matches the "function" statement.

[Eileen Miller]

Thank you!