MATLAB: Complex Number resulted in DOUBLE cannot convert the input expression into a double array

Question

I have done some digging and searching, but I cannot find solution for the particular error. I suspect it is the i acting as symbolic, but I am not sure. Below shows the code and the output. Please help me resolve this issue! Thank you!

Code:

A = [0 1
    -2 -3];
B=[0
   1];
tr = 0.5;
po = 0.05;
%zeta, omega, and z, w are to calculate damping and natural frequency
syms zeta omega;
[z, w] = solve([tr == (2.16 * zeta+0.6)/omega, po == exp(-1 *  zeta * pi / sqrt(1-zeta^2))], [zeta, omega]);
z = vpa(z,4)
w = vpa(w,4)
Poles = [-z*w+w*sqrt(z^2-1) -z*w-w*sqrt(z^2-1)]
place(A,B,Poles)

Output (error occurs at place):

Error using symengine
DOUBLE cannot convert the input expression into a double array.
If the input expression contains a symbolic variable, use VPA.

Answer 1

Use

z = double( vpa(z,4) );
w = double( vpa(w,4) );