error message when poles are in RHP

I have error message in this code when i have poles in RHP.

Attempted to access r2(2); index out of bounds because numel(r2)=1.

Error in B4 (line 46)
 wt = [0 r2(2) r2(1)] ;
 
 % PID stabilizing set
clear all;
 syms s;
 kp = sym('kp','real');
ki = sym('ki','real');
 kd= sym('kd','real');
w = sym('w','real');
 N = [595e07]; % Numerator
 D = [1 -972.2 4.34e6]; % Denominator
 tam_N = size(N);
 tam_D = size(D);
 n = tam_D (2) -1;
 m = tam_N (2) -1;
 ze = roots(N); % Zeros of N(s)
 l = 1;
 nz = 0;
 for k = 1:m
 if real(ze(k)) > 0
 nz = l; % RHP Zeros of N(s)
 l = l + 1;
 end
 end
 signature = n - m + 1 + 2*nz; % Signature number
 D_s = poly2sym(D,s); % D(s)
 N_s = poly2sym(N,s); % N(s)
 N_ms = subs(N_s , -s); % N(-s)
 Delta = s*D_s + (ki+kd*s^2)*N_s + kp*s*N_s; % ...Characteristic equation
 Delta = collect(Delta ,s); % simplify expression in ...terms of s
 V_s = collect(Delta*N_ms ,s); % V = Delta*N(-s)
 V = subs(V_s , 1i*w); % V(jw)
 Vr = real(V); % Real part of V
 Vi = imag(V); % Imaginary part of V
 for kp_f = -8.5:0.2:4.22 % Evaluate for a fixed Kp
 f_kp = subs(Vi , kp , kp_f); % substitute value of Kp
 f_Vi = sym2poly(f_kp); % convert to polynomial
 r = roots(f_Vi); % find the roots
 tam3 = size(r);
 l = 1;
 r2 = 0;
 for k = 1: tam3
 if imag(r(k)) == 0 && real(r(k)) > 0 % select ...real , positive roots
 r2(l) = real(r(k));
 l = l + 1;
 end
 end
 wt = [0 r2(2) r2(1)] ;
 tam_w = size(wt);
 R(1) = subs(Vr , w, wt(1));
 C1(1,:) = [0,coeffs(R(1)), 0];
 Te(1,:) = [0,ki ,0];
 R(tam_w (2)) = subs(Vr , w, wt(tam_w (2)));
 for k=2: tam_w (2)
 R(k) = subs(Vr , w, wt(k));
 [C1(k,:),Te(k,:)] = coeffs(R(k));
 end
 C1 = double(C1);
 A = -[C1(1 ,1) C1(1 ,2) 0;-C1(2 ,1) -C1(2 ,2) 0;C1(3 ,1) C1(3 ,2) 0]; % [kd ki kp]
 b = -[-C1(1 ,3);C1(2 ,3);-C1(3 ,3)];
 lb = [-300,-300, kp_f ];
 ub = [300 ,300 , kp_f ];
 plotregion(A,b,lb ,ub ,'y');
 hold on;
 axis equal
 xlabel('kd');
 ylabel('ki');
 zlabel('kp');
 end
 axis square;

Answer 1

[KALYAN ACHARJYA]

The problem is here

for k = 1: tam3
 if imag(r(k)) == 0 && real(r(k)) > 0 % select ...real , positive roots
 r2(l) = real(r(k));
 l = l + 1;
 end

In the code if condition doesnot hold true, hence, it unable to evaluate r2 array elemnets (It bypassing if condition). Therefore without r2(2) and r2(1), how can you assigned vaue to "wt"

 wt=[0 r2(2) r2(1)] ;

Till above for loop, r2=0 as predefined before the for loop, it consider r(1)=0 but what about r(2).

The solution is: Both Condition Must be Satisfied on imag(r(k)) == 0 and real(r(k))>0,

or

change the conditions.

Hoe you get the issue.