How I get eigenvalues from 4x4 matrix is positive?

This is my matlab code represent the my model

%Parameter Massa
m1 = 8095; % massa train set 1 dalam kg
m2 = 8500; % massa train set 2 dalam kg
g  = 10;

%Parameter Gaya
f1 = 205.10^3; % dalam N
f2 = 302.10^3; % dalam N

c_0_1 = 0.01176;
c_1_1 = 0.00077616;
c_2_1 = 4.48 ;

c_0_2 = 0.01176 ;
c_1_2 = 0.00077616;
c_2_2 = 4.48;

v_0 = 300;

hstar = 120;

a_1   = -1./m1.*(c_1_1 + 2.*c_2_1.*v_0);  
a_2   = -1./m2.*(c_1_2 + 2.*c_2_2.*v_0); 

a_1_head = 1-(a_1.*hstar);
a_2_head = 1-(a_2.*hstar);
b = 1;

p_1 = -1./m1.*(c_0_1 - c_2_1.*(v_0).^2);
p_2 = -1./m2.*(c_0_2 - c_2_2.*(v_0).^2);

A = [0  a_1_head      0        0;
     0     0          0        0;
     0 (a_2_head - 1) 0 a_2_head;
     0      0         0        0
     ];
 
B = [-b.*hstar         0;
      b                0;
      0        -b.*hstar;
     -b                b
     ];
 
U_t = [f1; f2;];
 
W = [((a_1 - 1).*v_0) - (p_1.*hstar);
     0;
     ((a_2 - 1).*v_0) - (p_2.*hstar);
     ((a_1 - 1).*v_0) - (p_1.*hstar);
     ];

C = [1 0 0 0;
     0 1 0 0;
     0 0 1 0;
     0 0 0 1;];

Q = [19999 0 0 0;
     0 19999 0 0;
     0 0 19999 0;
     0 0 0 19999;];

R = [599999999.9999 0;
     0 59999999.9999;];
 

I would like to find X, K ,L using icare

My goal to find all eigenvalues (L) from X matrix 4x4 is all positive > 0

 [X1,K1,L1] = icare(A,B,Q,R)

But I never get all eigenvalues positive

This is what i got

 X1 =

   1.0e+09 *

    0.0001    0.0206    0.0000    0.0002
    0.0206    5.7871    0.0170    2.3214
    0.0000    0.0170    0.0001    0.0169
    0.0002    2.3214    0.0169    2.3099


K1 =

    0.0058    1.6534   -0.0001   -0.0149
    0.0004    4.7137    0.0183    4.6848


L1 =

   -0.3283
   -0.4419
   -0.5336
   -2.1662