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

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.

[Walter Roberson]

Please show the complete error message.

One thing to remember is that vpa() does not convert the value to double precision, so your z and w stay symbolic after the vpa()

[Eric Wang]

Thank you for replying. The output, including Poles output is attached below.

Poles =

[ - 2.886 + 3.026i, - 2.886 - 3.026i]

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

Error in sym/double (line 588)
        Xstr = mupadmex('symobj::double', S.s, 0);

Error in sym/subsindex (line 735)
                X = double(A) - 1;

Error in sym/subsref (line 776)
            R_tilde = builtin('subsref',L_tilde,Idx);

Error in place (line 71)
   P = [P(~imag(P)) ; Pc ; conj(Pc)];

Answer 1

[Walter Roberson]

Use

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

[Eric Wang]

I apply the double() on the Poles variable and it works perfectly. Is it because vpa takes i as symbols, and applying double would convert it to imaginary number?

Thanks in advance

[Walter Roberson]

I am not sure. I think it might be because you build a vector of the vpa results and it might be having trouble converting symbolic vectors