Norm of transition matrix

It's a 2by2 transition matrix, and i'm writing the entries of the transition matrix as x_i here. A is the transition matrix with the four entries. Also, FYI, the norm of a transition matrix is the square root of the maximum eigenvalue of A(transpose)*A.

Below is my code, and somehow the graph is not showing anything. Could someone explain to me what i did wrong here?

odesys = @(t,x) [(0.1*cos(2*t)-0.1)*x(1) + x(3)*(-0.1*sin(2*t)+1); (0.1*cos(2*t)-0.1)*x(2)+x(4)*(-0.1*sin(2*t)+1);(-0.1*sin(2*t)-1)*x(1) + x(3)*(-0.1*cos(2*t)-0.1); (-0.1*sin(2*t)-1)*x(2)+x(4)*(-0.1*cos(2*t)-0.1)];
x0   = [1; 0; 0;1];                          
tspan = [0 50];                        
[t, x] = ode45(odesys, tspan, x0); 
A = [x(1) x(2);x(3) x(4)];
B = transpose(A);
C = mtimes(B,A);
b = max(eig(C));
plot(t, sqrt(b));
legend('norm', 'Location', 'NE')

Answer 1

[Walter Roberson]

for K = 1 : size(x,1);
    A = [x(K,1), x(K,2);x(K,3), x(K,4)];
    B = transpose(A);
    C = mtimes(B,A);
    b(K) = max(eig(C));
end

[Neil Xie]

Thank you so much!