Plotting graph with Alpha and spectral radius

hello

Answer 1

[Alan Stevens]

It works if you set i = 0.1:0.1:10. With i = 0; the inverse of S is full of Inf's.

[Alan Stevens]

You have to leave out i = 0. The following

A = [5 -1 0 0 0; -2 5 -1 0 0; 0 -2 5 -1 0; 0 0 -2 5 -1; 0 0 0 -2 5];
H = 0.5*(A+A');
S = 0.5*(A-A');
P_M=[];
alpha=[];
for i = [-0.5:0.1:-0.1 0.1:0.1:10]  % leave out i = 0
    alpha=[alpha i];
   s_radius=norm(eig(inv(i.*eye(5)+S)*(i.*eye(5)-H)*inv(i.*eye(5)+H)*(i.*eye(5)-S)),inf);
   P_M=[P_M s_radius];
end
plot(alpha,P_M), grid
xlabel('alpha'),ylabel('P M')

produces this for me:

[Alan Stevens]

In a previous comment you wrote "Unfortunately there is the same error but anyway i think i should set it as i = -0.5:0.1:10 as alpha is in the open set of 0-10.", which is why I set alpha from -0.5. However, if you just start i from 0.1 you should be able to get an appropriate graph.