How to use symsum function inside a function

Below I'm trying to write a small function, but I'm getting following error message

Unable to create a symbolic variable 'j' by using 'syms' inside a MATLAB function because 'j' is an existing function name, class name, method name, and so on. Use 'sym' instead.

the code is working outside the function module, I don't know the exact reason behind this? could someone explain me how to rectify this?

Thank yyou so much in advance

function [Area sigma]= Fractalblock(L0,t0,Rt,N,T);

syms j
Area= (L0*t0*symsum((4^(j+1))*((0.5)^j)*(Rt^j),j,0,N-1))-((t0^2)*symsum(2^(2*j+1)*(Rt^((2*j)-1)),j,1,N-1))-((t0^2)*symsum(2^(2*j+2)*Rt^(2*j),j,0,N-1));
sigma= area/T^2;

end

Answer 1

[Walter Roberson]

I have not seen that message before, but the work-around is

function [Area sigma]= Fractalblock(L0,t0,Rt,N,T);
    j = sym('j');
    Area= (L0*t0*symsum((4^(j+1))*((0.5)^j)*(Rt^j),j,0,N-1))-((t0^2)*symsum(2^(2*j+1)*(Rt^((2*j)-1)),j,1,N-1))-((t0^2)*symsum(2^(2*j+2)*Rt^(2*j),j,0,N-1));
    sigma= area/T^2;
end

You could have the same problem for i, j, pi, and eulergamma and possibly other names

syms does a hidden assignment to a variable, and when there are hidden assignments to a variable name that happens to be the same as the name of a function, then MATLAB is permitted to treat the name as a function, because MATLAB does static analysis instead of dynamic analysis.

[Chandra Sekhar Kommineni]

Thank you so much Mr. Roberson