Function 'gt' is not implemented for MuPAD symbolic objects

i want to find the solutions of this charactristric equation but i get the error'Function 'gt' is not implemented for MuPAD symbolic objects'.I know the reason is 'while' but i don't know how to solve this problem.

    nc=3.8;    ncl=3;
    c0=3*1e8;
    a=0.6*1e-6;

    syms u w n real 

    Jn=besselj(n,u);
    Jnp=diff(Jn,u);
    Kn=besselk(n,w);
    Knp=diff(Kn,w);

    J0=Jnp/(u*Jn);
    K0=Knp/(w*Kn);

    CHA=(J0+K0)*(J0+(ncl/nc)^2*K0)-n^2*(1/u^2+1/w^2)*(1/u^2+(ncl/nc)^2*1/w^2);
    Li=limit(CHA, w, 0); 

    v=zeros(1,10);
    for t=0:9
        dx=1;
        iter=0;  x=3;
        S=subs(Li,n,t);
        while abs(dx>0.0001)&& iter<200
            iter=iter+1;
            DC=-subs(S,u,x);
            Dif=diff(S,w);
            J=subs(Dif,u,x);
            dx=DC/J;
            x=x+dx;
        end
        v(t+1)=x;
    end
     EIGN_Frequency=v*c0*1e-14/(2*pi*a*sqrt(nc^2-ncl^2))

Answer 1

[Matt J]

Make sure dx does not become symbolic,

    dx=double(DC/J);