how to fix Summation index error?

hi every body.

my codes give me errors. plz help me to fix it.

clear;
syms x;
sy=[0 -1i;1i 0];
s=kron(sy,sy);
t=1;
de=50;
range1=0:0.1:10;
innerstate=[1 1 0 0;1 1 1 1;1 1 1 0;1 0 1 0];
ro=zeros(size(innerstate,1));
rov=zeros(size(innerstate,1));

Ha='[x/2 0 0 0;0 -x/2 x 0;0 x -x/2 0;0 0 0 x/2]';
Haf = str2func(sprintf('@(%s)%s;','x',Ha));
[vectors,values]=eig(Haf(x));

for n=1:size(innerstate,1)
    for m=1:size(innerstate,1)
        ro=ro+(vectors(:,m)*(vectors(:,n)'));
    end
end

symsum(symsum((vectors(:,m)*(vectors(:,n)')),m,1,4),n,1,4)

Error using sym/symsum (line 52)
Unable to compute sum with respect to '4'. Summation index must be
a symbolic variable.

Error in remove_shadow (line 22)
symsum(symsum((vectors(:,m)*(vectors(:,n)')),m,1,4),n,1,4)

Answer 1

[Sulaymon Eshkabilov]

Use this command:

symsum(symsum((vectors(:,m)*(vectors(:,n)'))))

instead of: symsum(symsum((vectors(:,m)*(vectors(:,n)')),m,1,4),n,1,4)